Sunday, July 7, 2013

Biochemistry Quiz (MCQs) and explanation

1.
Most major metabolic pathways are considered to be either mainly anabolic or catabolic. Which of the following pathways is most correctly considered to be amphibolic?

A. Lipolysis
B. Glycolysis
C. Oxidation of fatty acids
D. Citric acid cycle
E. Gluconeogenesis

2.
If a homogenate of liver cells is centrifuged to remove all cell membranes and organelles, which of the following enzyme activities will remain in the homogenate?

A. Glucose-6-phosphate dehydrogenase
B. Glycogen synthetase
C. Aconitase
D. Acyl CoA hydratase
E. Hydroxybutyrate dehydrogenase

3.
Which of the following is appropriate for a patient with renal failure?

A. High-carbohydrate diet
B. High-protein diet
C. Low-fat diet
D. High-fiber diet
E. Free water of at least 3 L per day

4.
An adolescent presents with abdominal discomfort, abdominal fullness, excess gas, and weight loss. Blood glucose, cholesterol, and alkaline phosphatase levels are normal. There is no jaundice or elevations. The stool tests positive for reducing substances. Which of the following is the most likely diagnosis?

A. Diabetes mellitus
B. Starvation
C. Nontropical sprue
D. Milk intolerance
E. Gallstones

5.
Juvenile diabetes mellitus is a disorder of carbohydrate metabolism caused by insulin deficiency. The disease often follows a viral infection with inflammation of the pancreatic   cells, but also exhibits genetic predisposition with a 40 to 50% concordance rate in monozygous twins and clustering in families. Juvenile diabetes mellitus is best described as what type of disorder?’

A. Congenital disorder
B. Multifactorial disorder
C. Mendelian disorder
D. Sporadic disorder
E. Sex-limited disorder

6.
A couple is referred to the physician because their first three pregnancies have ended in spontaneous abortion. Chromosomal analysis reveals that the wife has two cell lines in her blood, one with a missing X chromosome (45,X) and the other normal (46,XX). Which of the following is the best description of her chromosomal constitution?

A. Chimeric
B. Monoploid
C. Trisomic
D. Mosaic
E. Euploid

7.
A child with cleft palate, a heart defect, and extra fifth fingers is found to have 46 chromosomes with extra material on one homologue of the chromosome 5 pair. This chromosomal abnormality is best described by which of the following terms?

A. Polyploidy
B. Balanced rearrangement
C. Ring formation
D. Mosaicism
E. Unbalanced rearrangement

8.
A 10-year-old boy is referred to the physician because of learning problems and a lack of motivation in school. His family history is unremarkable. Physical examination is normal except for single palmar creases of the hands and curved fifth fingers (clinodactyly). The physician decides to order a karyotype. Which of the following indications for obtaining a karyotype would best explain the physician's decision in this case?

A. A couple with multiple miscarriages, or a person who is at risk for an inherited chromosome rearrangement
B. A child with ambiguous genitalia who needs genetic sex assignment
C. A child with an appearance suggestive of Down's syndrome or other chromosomal disorder
D. A child with mental retardation and/or multiple congenital anomalies
E. A child who is at risk for

9.
Chromosomal analysis reveals a 47,XYY karyotype. Which of the following descriptions best fits this abnormality?

A. Autosomal trisomy
B. A male with Klinefelter's syndrome
C. Sex chromosome aneuploidy
D. A female with Turner's syndrome
E. Sex chromosome triploidy

10.
Which of the following karyotypes is an example of aneuploidy?
A. 46,XX
B. 23,X
C. 69,XXX
D. 92,XXXX
E. 90,XX

11.
Which of the following is the proper cytogenetic notation for a female with Down's syndrome mosaicism?
A. 46,XX,+21/46,XY
B. 47,XY,+21
C. 47,XXX/46,XX
D. 47,XX,+21/46,XX
E. 47,XX,+21(46,XX)

12.
A newborn girl is found to have marked swelling of the dorsal areas of her feet along with a broad (webbed) neck, a broad chest, and a heart murmur that is due to coarctation of the aorta. Her physician suspects a chromosomal disorder and orders a karyotype. Which of the results pictured below is most likely? 


A. Result A
B. Result B
C. Result C
D. Result D

13.
A 2-week-old baby is hospitalized for inadequate feeding and poor growth. The parents are concerned by the child's weak cry. An experienced grandmother accompanies them, saying she thought the cry sounded like a cat's meow. The grandmother also states that the baby doesn't look much like either parent. The physician orders a karyotype after noting a small head size (microcephaly) and subtle abnormalities of the face. Which of the results pictured below is most likely? 

A. Result A
B. Result B
C. Result C
D. Result D
E. Result E

14.
A child with cleft palate, a heart defect, and extra fifth fingers is found to have 46 chromosomes with extra material on one homologue of the chromosome 5 pair. This chromosomal abnormality is best described by which of the following terms?

A.Polyploidy 
B.Balanced rearrangement 
C.Ring formation 
D.Mosaicism 
E.Unbalanced rearrangement 

15.
A 10-year-old boy is referred to the physician because of learning problems and a lack of motivation in school. His family history is unremarkable. Physical examination is normal except for single palmar creases of the hands and curved fifth fingers (clinodactyly). The physician decides to order a karyotype. Which of the following indications for obtaining a karyotype would best explain the physician's decision in this case?

A. A couple with multiple miscarriages, or a person who is at risk for an inherited chromosome rearrangement 
B. A child with ambiguous genitalia who needs genetic sex assignment 
C. A child with an appearance suggestive of Down's syndrome or other chromosomal disorder 
D. A child with mental retardation and/or multiple congenital anomalies 
E. A child who is at risk for cancer 

16.
Chromosomal analysis reveals a 47,XYY karyotype. Which of the following descriptions best fits this abnormality?

A.Autosomal trisomy 
B.A male with Klinefelter's syndrome 
C.Sex chromosome aneuploidy 
D.A female with Turner's syndrome 
E.Sex chromosome triploidy 

17.
Which of the following karyotypes is an example of aneuploidy?

A.46,XX 
B.23,X 
C.69,XXX 
D.92,XXXX 
E.90,XX 

18.
Which of the following is the proper cytogenetic notation for a female with Down's syndrome mosaicism?

A.46,XX,+21/46,XY 
B.47,XY,+21 
C.47,XXX/46,XX 
D.47,XX,+21/46,XX 
E.47,XX,+21(46,XX) 

19.
Gardner's syndrome is an autosomal dominant condition characterized by multiple polyps of the intestines, bony tumors, skin cysts, and a high risk of intestinal cancer. A family is encountered in which a great-grandfather, grandmother, and father are affected with Gardner's syndrome and develop intestinal cancer in their thirties. The father brags that none of his four children have inherited Gardner's syndrome because they lack skin cysts and have not had cancer. The chance that at least one child has inherited the Gardner's syndrome allele, and the reason the children have not manifested cancer, are

A.1/4, ascertainment bias 
B.1/2, variable cancer predisposition 
C.3/4, early-onset disease manifestation 
D.13/16, incomplete medical evaluation 
E.15/16, later-onset disease manifestation 

20.
Ectrodactyly is an autosomal dominant trait that causes missing middle fingers (lobster claw malformation). A grandfather and grandson both have ectrodactyly, but the intervening father has normal hands by x-ray. Which of the following terms applies to this family?

A.Incomplete penetrance 
B.New mutation 
C.Variable expressivity 
D.Germinal mosaicism 
E.Anticipation 

ANSWERS

1. D

In general, the corresponding pathways of catabolism and anabolism are not identical (glycolysis versus gluconeogenesis, lipolysis and  oxidation of fatty acids versus fatty acid synthesis and lipogenesis, glycogenolysis versus glycogenesis). However, the citric acid cycle is a central pathway from which anabolic precursors of biosynthetic reactions may derive or into which the complete catabolism of small molecules to carbon dioxide and water may occur. For these reasons, the citric acid cycle is often called an amphibolic pathway. 

2. A

Centrifugation of a cellular homogenate at a force of 100,000 × g will pellet all cellular organelles and membranes. Only soluble cellular molecules found in the cytosol will remain in the supernatant. Thus, the enzymes of glycolysis and most of those of gluconeogenesis, fatty acid synthesis, and the pentose phosphate pathway will be in the supernatant. Glucose-6-phosphate dehydrogenase, which results in the formation of 6-phosphoglucono- -lactone from glucose-6-phosphate, is the committed step in the pentose phosphate pathway. In the pellet will be the enzymes within mitochondria, including those of the citric acid cycle (aconitase), fatty acid  oxidation (acyl CoA hydratase), and ketogenesis (hydroxybutyrate dehydrogenase). Enzymes of glycogen degradation and synthesis (glycogen synthetase) will also be in the pellet associated with glycogen particles. 

3. A

A diet high in carbohydrate and fats spares glucose use and inhibits gluconeogenesis, thereby preventing protein catabolism and nitrogen production. A major function of the kidneys is to excrete nitrogen catabolized from proteins in the form of urea. Indeed, the major clinical measures of renal function are products of protein catabolism [blood urea nitrogen (BUN) and blood creatinine]. A diet for a patient with renal failure should therefore minimize protein and nitrogen load. Although 3 L/day of fluid is a normal intake for adults with healthy kidneys, glomerular filtration and water excretion are decreased in renal failure. Water and salt intake (particularly potassium) must therefore be limited in renal failure. Excess water or salt intake in patients with renal disease is manifest clinically by edema (swollen eyelids, swollen lower limbs). 

4. D

Milk intolerance may be due to milk protein allergies during infancy, but it is commonly caused by lactase deficiency in older individuals. Intestinal lactase hydrolyzes the milk sugar lactose into galactose and glucose, both reducing sugars that can be detected as reducing substances in the stool. The symptoms of lactose intolerance (lactase deficiency) and other conditions involving intestinal malabsorption include diarrhea, cramps, and flatulence due to water retention and bacterial action in the gut. In nontropical sprue, symptoms seem to result from the production of antibodies in the blood against fragments of wheat gluten. It seems likely that a defect in intestinal epithelial cells allows tryptic peptides from the digestion of gluten to be absorbed into the blood, as well as to exert a harmful effect on intestinal epithelia. 

Gallbladder inflammation (cholecystitis) usually presents with acute abdominal pain (colic) with radiation to the right shoulder. The normal composition of bile is about 5% cholesterol, 15% phosphatidylcholine, and 80% bile salt in a micellar liquid form. Increased cholesterol from high-fat diets or genetic conditions can upset the delicate micellar balance, leading to supersaturated cholesterol or cholesterol precipitates that cause gallstone formation. Removal of the gallbladder is a common treatment for this painful condition. 

Mobilization of fats with the production of ketone bodies occurs during fasting and starvation, but ketone production is well controlled. During uncontrolled diabetes mellitus, ketogenesis proceeds at a rate that exceeds the buffering capacity of the blood to produce ketoacidosis.

5. B

Many common diseases are caused by a combination of environmental and genetic factors, and are described as multifactorial diseases. Examples include diabetes mellitus, schizophrenia, alcoholism, and many common birth defects such as cleft palate or congenital dislocation of the hip. The proportion of genetically identical monozygous twins who share a trait such as diabetes mellitus provides a measure of the genetic contribution to etiology (hereditability). Mendelian disorders are completely determined by the genotype of an individual, and exhibit 100% concordance in identical twins. Sporadic disorders have no genetic predisposition and do not cluster in families except by chance or through similar environmental exposure. Congenital disorders are present at birth, in contrast to juvenile diabetes mellitus, which usually presents during childhood. Sex-limited disorders occur predominantly in males or females, in contrast to the approximately equal sex distribution of juvenile diabetes mellitus. 

6. D

The case described represents one of the more common chromosomal causes of reproductive failure, Turner mosaicism. Turner's syndrome represents a pattern of anomalies including short stature, heart defects, and infertility. Turner's syndrome is often associated with a 45,X karyotype (monosomy X) in females, but mosaicism (i.e., two or more cell lines with different karyotypes in the same individual) is common. However, chimerism (i.e., two cell lines in an individual arising from different zygotes, such as fraternal twins who do not separate) is extremely rare. Trisomy refers to three copies of one chromosome, euploidy to a normal chromosome number, and monoploidy to one set of chromosomes (haploidy in humans). 

7. E

Chromosomal abnormalities may involve changes in number (i.e., polyploidy and aneuploidy) or changes in structure (i.e., rearrangements such as translocations, rings, and inversions). Extra material (i.e., extra chromatin) seen on chromosome 5 implies recombination of chromosome 5 DNA with that of another chromosome to produce a rearranged chromosome. Since this rearranged chromosome 5 takes the place of a normal chromosome 5, there is no change in number of the autosomes (nonsex chromosomes) or sex chromosomes (X and Y chromosomes). The question implies that all cells karyotyped from the patient (usually 11 to 25 cells) have the same chromosomal constitution, ruling out mosaicism. The patient's clinical findings are similar to those occurring in trisomy 13, suggesting that the extra material on chromosome 5 is derived from chromosome 13, producing an unbalanced karyotype called dup(13) or partial trisomy 13. 

8. D

The hallmarks of children with chromosomal anomalies are mental retardation and multiple congenital anomalies. In this case, the individual has learning problems that have not yet been recognized as mental retardation, and he has minor anomalies rather than major birth defects that cause cosmetic or surgical problems. The physician was astute to suspect a chromosomal anomaly even when the developmental disability and alterations in physical appearance were subtle. Other indications for a karyotype include a couple with multiple miscarriages, an individual at risk for inheriting or transmitting a chromosomal rearrangement, a child with ambiguous external genitalia, or an individual with characteristics of a chromosomal syndrome such as Down's, Turner's, or Klinefelter's syndrome. Chromosome translocations are characteristic of many types of cancer, but these occur in somatic cancer cells rather than in the patient's germ line. 

9. C

The 47,XYY karyotype is an example of sex chromosome aneuploidy, as are Klinefelter's syndrome (47,XXY), Turner's syndrome (45,X), and triple X syndrome (47,XXX). Sex chromosome mixoploidy implies mosaicism, such as 45,X/46,XX with two cell lines in one individual. Autosomal trisomies include Down's syndrome [47,XX+21 (trisomy 21)], Patau's syndrome [47,XX+13 (trisomy 13)], and Edwards' syndrome [47,XY+18 (trisomy 18)].

10. E

Aneuploidy involves extra or missing chromosomes that do not arise as increments of the haploid chromosome number n. Polyploidy involves multiples of n, such as triploidy (3n = 69,XXX) or tetraploidy (4n = 92,XXXX). Diploidy (46,XX) and haploidy (23,X) are normal karyotypes in gametes and somatic cells, respectively. A 90,XX karyotype represents tetraploidy with two missing X chromosomes, which has been seen in one patient who had features that resembled those of Turner's syndrome.

11. D

Mosaicism occurs when a chromosomal anomaly affects one of several precursor cells of an embryo or tissue. The two or more karyotypes that characterize the mosaic cells are separated by a slash in cytogenetic notation. The notation 47,XX,+21 denotes a cell line typical of a female with trisomy 21 (Down's syndrome), while 46,XX is the karyotype expected for a normal female. 

12. A

A chromosome study or karyotype delineates the number and kinds of chromosomes in one cell karyon (nucleus). Blood is conveniently sampled, so most chromosomal studies or karyotypes are performed on peripheral leukocytes in blood. A number of leukocytes are karyotyped under the microscope (10 to 25, depending on the laboratory), and a representative photograph is taken. The chromosome images are then arranged (cut out by hand or moved by computer) in order of size from the #1 pair to the #22 pair, and this ordered array is also called a karyotype. Except in cases of mosaicism (different karyotypes in different tissues), the peripheral blood karyotype is indicative of the germ-line karyotype that is characteristic for an individual. In most cases of Turner's syndrome there is a lack of one X chromosome, as in panel A, which shows one X (arrow) and no Y chromosome. Other cases involve mosaicism (45,X/46,XX or 45,X/46,XY) or isochromosomes (e.g., 46,X,isoXq). Correlation of karyotypes and phenotypic features of girls with Turner's syndrome has demonstrated that haploinsufficiency (partial monosomy) of the short arm (Xp) is what generates the characteristic manifestations (web neck, shield chest, puffy feet, coarctation). Women with Turner's syndrome also have short stature and infertility due to maldevelopment of the ovaries (streak gonads). 

13. E

Children with chromosome abnormalities often exhibit poor growth (failure to thrive) and developmental delay with an abnormal facial appearance. This baby is too young for developmental assessment, but the catlike cry should provoke suspicion of cri-du-chat syndrome. Cri-du-chat syndrome is caused by deletion of the terminal short arm of chromosome 5 [46,XX,del(5p), also abbreviated as 5p–] as depicted in panel e. When a partial deletion or duplication like this one is found, the parents must be karyotyped to determine if one carries a balanced reciprocal translocation. The other karyotypes show (a) deletion of the short arm of chromosome 4 [46,XY,del(4p) or 4p–]; (b) XYY syndrome (47,XYY); (c) deletion of the long arm of chromosome 13 [46,XX,del(13q) or 13q–]; (d) Klinefelter's syndrome (47,XXY). Most disorders involving excess or deficient chromosome material produce a characteristic and recognizable phenotype (e.g., Down's, cri-du-chat, or Turner's syndrome). The deletion of 4p– (panel A) produces a pattern of abnormalities (syndrome) known as Wolf-Hirschhorn syndrome; deletion of 13q– produces a 13q– syndrome (no eponym). The mechanism(s) by which imbalanced chromosome material produces a distinctive phenotype is completely unknown.

14. E

Chromosomal abnormalities may involve changes in number (i.e., polyploidy and aneuploidy) or changes in structure (i.e., rearrangements such as translocations, rings, and inversions). Extra material (i.e., extra chromatin) seen on chromosome 5 implies recombination of chromosome 5 DNA with that of another chromosome to produce a rearranged chromosome. Since this rearranged chromosome 5 takes the place of a normal chromosome 5, there is no change in number of the autosomes (nonsex chromosomes) or sex chromosomes (X and Y chromosomes). The question implies that all cells karyotyped from the patient (usually 11 to 25 cells) have the same chromosomal constitution, ruling out mosaicism. The patient's clinical findings are similar to those occurring in trisomy 13, suggesting that the extra material on chromosome 5 is derived from chromosome 13, producing an unbalanced karyotype called dup(13) or partial trisomy 13.

15. D

The hallmarks of children with chromosomal anomalies are mental retardation and multiple congenital anomalies. In this case, the individual has learning problems that have not yet been recognized as mental retardation, and he has minor anomalies rather than major birth defects that cause cosmetic or surgical problems. The physician was astute to suspect a chromosomal anomaly even when the developmental disability and alterations in physical appearance were subtle. Other indications for a karyotype include a couple with multiple miscarriages, an individual at risk for inheriting or transmitting a chromosomal rearrangement, a child with ambiguous external genitalia, or an individual with characteristics of a chromosomal syndrome such as Down's, Turner's, or Klinefelter's syndrome. Chromosome translocations are characteristic of many types of cancer, but these occur in somatic cancer cells rather than in the patient's germ line.

16. C

The 47,XYY karyotype is an example of sex chromosome aneuploidy, as are Klinefelter's syndrome (47,XXY), Turner's syndrome (45,X), and triple X syndrome (47,XXX). Sex chromosome mixoploidy implies mosaicism, such as 45,X/46,XX with two cell lines in one individual. Autosomal trisomies include Down's syndrome [47,XX+21 (trisomy 21)], Patau's syndrome [47,XX+13 (trisomy 13)], and Edwards' syndrome [47,XY+18 (trisomy 18)].

17. E

Aneuploidy involves extra or missing chromosomes that do not arise as increments of the haploid chromosome number n. Polyploidy involves multiples of n, such as triploidy (3n = 69,XXX) or tetraploidy (4n = 92,XXXX). Diploidy (46,XX) and haploidy (23,X) are normal karyotypes in gametes and somatic cells, respectively. A 90,XX karyotype represents tetraploidy with two missing X chromosomes, which has been seen in one patient who had features that resembled those of Turner's syndrome.

18. D

Mosaicism occurs when a chromosomal anomaly affects one of several precursor cells of an embryo or tissue. The two or more karyotypes that characterize the mosaic cells are separated by a slash in cytogenetic notation. The notation 47,XX,+21 denotes a cell line typical of a female with trisomy 21 (Down's syndrome), while 46,XX is the karyotype expected for a normal female.

19. E

The father is affected with Gardner's syndrome (175100), an autosomal dominant disease. Therefore, each of his four children has a 1/2 chance of receiving the allele that causes Gardner's syndrome and a 1/2 chance of receiving the normal allele. The probability that none of his four children received the allele for Gardner's syndrome is thus the joint probability of four independent events, computed by the product 1/2 × 1/2 × 1/2 × 1/2 = 1/16. The probability that at least one child has received the abnormal Gardner's syndrome allele is thus 1 – 1/16 = 15/16. Gardner's syndrome is one of many genetic disorders that may not be obvious in early childhood. Intestinal cancer in particular has a later onset, with 50% of patients being affected by age 30 to 35. More extensive evaluation of the children for internal signs of disease (e.g., the bony tumors) is required before the father can conclude that he has not transmitted the gene. Late-onset disorders are an important category of adult genetic disease, and presymptomatic testing for these diseases is a novel application of DNA diagnosis.

20. A


Incomplete penetrance applies to a normal individual who is known from the pedigree to have an allele responsible for an autosomal dominant trait. Variable expressivity refers to family members who exhibit signs of the autosomal dominant disorder that vary in severity. When this severity seems to worsen with progressive generations, it is called anticipation. A new mutation in the grandson would be extremely unlikely given the affected grandfather. The father could be an example of somatic mosaicism if a back-mutation occurred to allow normal limb development, but there is no reason to suspect mosaicism of his germ cells (germinal mosaicism).

Wednesday, July 3, 2013

Neuroscience Quiz (MCQs) with explanation

1. 
The proper sensory nucleus is derived from which of the following

A.Alar plate 
B.Basal plate 
C.Sulcus limitans 
D.Neural crest 
E.Roof plate 
F.Mesencephalon 
G.Floor plate 
H.Rathke's pouch 
I.Rhombic lips

2.
A brain MRI scan taken from a 6-month-old baby revealed that while the overall size of the cerebral cortex was normal, the size of the pyramidal tracts was considerably smaller than normal. Which of the following is the most likely explanation for this defect

A.Reduction in the numbers of cortical neurons giving rise to pyramidal tract fibers 
B.Reduction in the numbers of synaptic contacts made by pyramidal tract neurons 
C.Reduction in the extent of myelin found on pyramidal tract neurons 
D.Reduction in the amount of neurotransmitter released by pyramidal tract neurons 
E.Reduction in the numbers of glial cells attached to pyramidal tract neurons

3.
Which of the following is the most ubiquitous excitatory neurotransmitter in the brain?

A.ACh 
B.Glutamate 
C.Norepinephrine 
D.Dopamine 
E.Substance P 

4.
Epileptiform activity is believed to include the activation of which of the following

A.GABA receptors 
B.Glutamate receptors 
C.Nicotinic receptors 
D.Serotonin receptors 
E.Glycine receptors

5.
Which of the following enzymes is directly responsible for the degradation of norepinephrine

A.Tryptophan hydroxylase 
B.Tyrosine hydroxylase 
C.Dopamine  -hydroxylase 
D.Catechol-O-methyltransferase 
E.Choline acetyltransferase

6.
Bladder functions are regulated by which of the following combinations of inputs

A.Vagal and sacral efferent fibers only 
B.Vagal, sacral, and descending fibers from the cerebral cortex 
C.Lumbar and sacral efferent fibers only 
D.Lumbar, sacral, and descending fibers from the cerebral cortex 
E.Lumbar, thoracic, and cervical fibers only

7.
Synthesis and storage of norepinephrine can be prevented by which of the following substances

A.Guanethidine sulfate 
B.Reserpine 
C.Phenoxybenzamine hydrochloride 
D.Hexamethonium chloride 
E.Metoprolol 

8.
A 43-year-old male is recovering from an infectious disease and experiences a marked instability in his blood pressure with episodes of spiking of blood pressure. After a series of extensive examinations, it was concluded that this disorder was due to the effects of the infectious agent upon a component of the peripheral nervous system. Logical sites where an infectious agent could produce such an effect include which of the following

A.Superior ganglia of cranial nerves IX and X 
B.Geniculate and trigeminal ganglia 
C.Otic and superior salivatory ganglia 
D.Carotid sinus and aortic arch 
E.Carotid and aortic bodies 

9.
The lesion at B would most likely result in which of the following deficits? 

 A.Paralysis of the contralateral limbs 
 B.Loss of conscious proprioception of the contralateral side of the body 
 C.Nystagmus 
 D.Lateral gaze paralysis 
 E.Facial paralysis

10.
A patient with the lesion at A will generally show which of the following deficits? 


 A.Partial blindness 
 B.Loss of ability to gaze medially 
 C.Loss of ability to show tracking movements 
 D.Loss of accommodation reflex 
 E.Nystagmus

11.
A person is told that he has astigmatism. To correct this defect, the optometrist prescribes which of the following lenses

A.Cylindrical lens because the cornea or lens is oblong 
B.Concave lens because the eyeball is too long 
C.Convex lens because the lens is too short 
D.Neutral lens because the eyeball is normal but the cornea is too thin 
E.Concave lens because the cornea is opaque

12.
As a result of calcification of the internal carotid artery, which impinges upon the lateral half of the right optic nerve prior to its entrance to the brain of a 68-year-old woman, resulting in certain visual deficits. Which of the following is the most likely visual deficits

A.Total blindness of the right eye 
B.Right nasal hemianopsia 
C.Right homonymous hemianopsia 
D.Right bitemporal hemianopsia 
E.Right upper homonymous quadrantanopia

13.
A 55-year-old woman complains of headaches and is subsequently diagnosed as having a tumor localized to the left parietal lobe. In addition to a variety of sensory deficits, further examination also reveals a reduction in her visual fields. Which of the following is the most likely visual deficit

A.Left homonymous hemianopsia 
B.Right homonymous hemianopsia 
C.Left upper quadrantanopia 
D.Right upper quadrantanopia 
E.Right lower quadrantanopia 

14.
The conscious perception of movement is mediated by which of the following receptors

 A.Meissner's corpuscles 
 B.Free nerve endings 
 C.Merkel's receptors 
 D.Joint capsules 
 E.Pacinian corpuscles 

15.
An impairment in the ability to perform certain types of learned, complex movements (referred to as apraxia) usually results from a lesion of which of the following?

 A.Precentral gyrus 
 B.Postcentral gyrus 
 C.Premotor cortex 
 D.Prefrontal cortex 
 E.Cingulate gyrus 

16.
Which of the following is the primary transmitter released from terminals of both neostriatal and paleostriatal neurons?

 A.Glycine 
 B.Enkephalin 
 C.Dopamine 
 D.GABA 
 E.Glutamate 

17.
The neurotoxin 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) has recently been applied experimentally with considerable success as a model for which of the following?

 A.Huntington's disease 
 B.Hemiballism 
 C.Parkinson's disease 
 D.Tardive dyskinesia 
 E.Dystonia 

18.
 A man presents with a wide-based, ataxic gait during his attempts at walking. He also is unsteady and sways when standing and displays a tendency to fall backward or to either side in a drunken manner. A lesion is most likely located in which of the following?

 A.Hemispheres of the posterior cerebellar lobe 
 B.Anterior limb of the internal capsule 
 C.Dentate nucleus 
 D.Anterior lobe of the cerebellum 
 E.Flocculonodular lobe of the cerebellum

19.
Which one of the following thalamic nuclei makes local connections with other thalamic nuclei and, additionally, projects to the basal ganglia

 A.Centromedian thalamic nucleus 
 B.Medial geniculate thalamic nucleus 
 C.Lateral geniculate thalamic nucleus 
 D.Dorsomedial thalamic nucleus 
 E.Anterior thalamic nucleus 
 F.Pulvinar 

20.
The supraoptic nucleus is most closely associated with which of the following?

 A.Feeding behavior 
 B.Temperature regulation 
 C.Sexual behavior 
 D.Short-term memory functions 
 E.Water balance 

21.
Lesions of the lateral hypothalamus will likely produce which of the following

 A.Feeding behaviors 
 B.Drinking behaviors 
 C.Sexual behaviors 
 D.Aphagia 
 E.Hypertension

22.
A number of investigations have provided strong evidence that the suprachiasmatic nucleus plays an important role in which of the following

 A.Water intake 
 B.Food intake 
 C.Hypertension 
 D.Circadian rhythms 
 E.Short-term memory 

23.
The CT scan below reveals that the patient has a glioma (T) on the right side of the brain. It is likely that the patient has sustained which of the following? 



 A.A UMN paralysis of the left side 
 B.Dyskinesia 
 C.Intention tremor 
 D.Upper left quadrantanopia 
 E.Upper right quadrantanopia 

24.
Question 1 of 4
A lesion of which region in the diagram below will likely result in receptive aphasia?


A.A
B.B 
C.C 
D.D 
E.E 
F.F 
G.G 
H.H 

25.
Question 1 of 2
An individual who complains about disruption in limb muscle function is diagnosed with a disorder in which the transmitter released at the neuromuscular junction is not removed from the synaptic cleft. 

Which of the following is the primary mechanism involved in removal of the transmitter at the neuromuscular junction

 A.Enzymatic degradation 
 B.Diffusion 
 C.Reuptake 
 D.Actions of antibodies 
 E.Distribution of sodium and potassium ions along muscle membrane 

Question 2 of 2
An individual who complains about disruption in limb muscle function is diagnosed with a disorder in which the transmitter released at the neuromuscular junction is not removed from the synaptic cleft. 

Which of the following enzymes is required for the metabolism of the transmitter at the neuromuscular junction

 A.Choline acetyltransferase 
 B.Glutaminase 
 C.Glutamine synthetase 
 D.Acetylcholinesterase 
 E.Serine hydroxymethyltransferase 

               ANSWERS

1- A
Structures associated with sensory functions, such as the proper sensory nucleus and the spinal nucleus of cranial nerve V, are derived from the alar plate

2- C
Extensive myelination occurs in postnatal development. The failure of the pyramidal tracts to form myelin would account for the reduction in their size. In this particular situation, the size of the cerebral cortex was approximately normal, suggesting that there was no significant decrease in cortical cells. Variation in the numbers of synaptic contacts, transmitter formation, and glial cells would not account for a reduction in the size of the pyramidal tract

3- B
The largest numbers of excitatory synapses in the CNS are mediated by glutamate as it is believed that approximately half of the synapses in the brain release glutamate. For example, functions mediated by fibers that originate from the cerebral cortex and descend to such regions as the neostriatum, thalamus, brainstem, and spinal cord are generally believed to be mediated by glutamate. Many other neuronal systems throughout the brain and spinal cord utilize glutamate as well. Dopaminergic and noradrenergic neurons, while mostly excitatory, can also be inhibitory at some synapses and are less numerous than glutamate. Cholinergic and substance P synapses are also excitatory, but are likewise less numerous than glutamate.

4- B
Excitatory amino acids and, in particular, the glutamate family of compounds have long been thought to play an important role in epileptiform activity. Epileptiform activity typically includes AMPA-receptor activation. However, as the seizure becomes more intense, there is increased involvement of NMDA receptors. This is evidenced by the facts that NMDA antagonists can reduce the intensity and length of the seizure activity and that, following removal of human epileptic hippocampal tissue, there is an up-regulation of both AMPA and NMDA receptors. Metabotropic glutamate receptors have been shown to be present in the retina but have not yet been demonstrated to be present in regions of the brain that are typically epileptogenic. GABA and glycine are inhibitory transmitters; therefore, seizures would logically block such receptor activation. There has been no substantive evidence concerning the role of cortical nicotinic receptors in epilepsy.

5- D
Tryptophan hydroxylase, tyrosine hydroxylase, and choline acetyltransferase are enzymes that are critical for the biosynthesis of serotonin, catecholamines, and ACh, respectively. Dopamine  -hydroxylase converts dopamine to norepinephrine. Catechol-O-methyltransferase and monoamine oxidase are critical for the metabolic degradation of catecholamines

6- D
The smooth muscle of the bladder is innervated by postganglionic fibers of the sympathetic nervous system that arise from the inferior mesenteric ganglion. This ganglion, in turn, receives its inputs from T12–L2 of the intermediolateral cell column of the spinal cord. The smooth muscle of the bladder also receives inputs from postganglionic parasympathetic fibers that are innervated by preganglionic fibers arising from S2–S4. The external sphincter of the bladder (striated muscle) is innervated by ventral horn cells from the spinal cord. These ventral horn cells, in turn, receive inputs from supraspinal neurons that arise, in part, from the cerebral cortex. It is these neurons that form a part of the substrate for voluntary control over bladder functions.

7- B
Noradrenergic activity can be blocked by a number of mechanisms. Reserpine, for example, prevents the synthesis and storage of norepinephrine in sympathetic nerve terminals. Guanethidine sulfate affects noradrenergic transmission by blocking the release of norepinephrine at the sympathetic endings. Competitive  -receptor blockers include phenoxybenzamine hydrochloride and phentolamine, whereas metoprolol blocks  1 receptors. Since ACh is the transmitter at preganglionic synapses of both the parasympathetic and sympathetic nervous systems, hexamethonium chloride is an effective ganglionic blocker at these synapses.

8- D
Specialized peripheral receptors, which specifically respond to changes in blood pressure, include the carotid sinus (associated with cranial nerve IX) and the aortic arch (associated with cranial nerve X). If these receptors (or the cell bodies associated with these receptors) are damaged, then one of the fundamental regulatory mechanisms for the control of blood pressure would be disrupted. The results of such a disruption would likely lead to increases and instability in blood pressure with evidence of spiking of blood pressure. Because these sensory receptors in these structures respond to increases in blood pressure, they are, in effect, stretch receptors and are consequently referred to as baroreceptors. The principal projection of the axons associated with these baroreceptors is the solitary nucleus of the medulla, which in turn, projects to autonomic nuclei such as the dorsal motor nucleus of the vagus nerve, ventrolateral medulla, and higher regions associated with autonomic functions, which include the PAG, hypothalamus, and limbic system.

9- A
Since the lesion is restricted to the medial aspect of the basilar part of the pons, the corticospinal tract would be affected, producing paralysis of the contralateral limbs. Although other structures would also be affected and could produce additional deficits, such deficits are not listed in this question. The other dysfunctions listed would not occur because they are associated with structures situated in the pontine tegmentum, which is not included in this lesion.

10- C
The lesion involves the superior colliculus. This structure receives inputs from the cerebral cortex and optic tract and its neurons respond to moving objects in the visual field. It is considered essential for the regulation of tracking movements. Lesions of the superior colliculus have not been shown to produce any of the other deficits listed in this question. Nystagmus is not likely to occur because the lesion does not involve the medial longitudinal fasciculus or the pontine gaze center.

11- A
In astigmatism, the shapes of the cornea and possibly the lens become oblong, resulting in differences in the curvature of the lens along the long and short axes. Thus, astigmatism is corrected with a cylindrical lens.

12- B
Calcification of the internal carotid artery could serve to disrupt nerve fibers proximal to it. One such group of fibers includes parts of the optic nerve. In this case, the component of the right optic nerve affected includes the lateral aspect, or those fibers that mediate vision associated with the nasal visual field of the right eye. If the damage were more extensive and if it involved the entire nerve, then total blindness of the right eye would have occurred.

13- E
Fibers from the left lateral geniculate destined for the upper bank of the calcarine fissure will mediate visual impulses associated with lower quadrants of the right visual fields for both eyes. This deficit is referred to as a right lower quadrantanopia.

14- D
Meissner's corpuscles, Merkel's receptors, and pacinian corpuscles respond to tactile, pressure, or possibly vibratory stimuli, while free nerve endings are associated with nociceptive stimuli. Joint capsules respond to movement of the limb, and the axons of these receptors contribute to the dorsal column–medial lemniscal system mediating the conscious perception of movement.

15- C
The premotor areas play an important role in the programming or sequencing of responses that compose complex learned movements. They receive significant inputs for this process from the posterior parietal lobule and, in turn, signal appropriate neurons in the brainstem and spinal cord (both flexors and extensors). Lesions of the postcentral gyrus produce a somatosensory loss. Lesions of the precentral gyrus produce paralysis. Neither lesions of the prefrontal cortex nor those of the cingulate gyrus have been reported to produce apraxia.

16- D
The major transmitter released at terminals of neostriatal and paleostriatal fibers is GABA. Thus, the output of the basal ganglia is mainly inhibitory. This suggests that thalamic influences upon the cortex are generated through the process of disinhibition, whereby neurons of the basal ganglia are inhibited. The presence of glycine in striatal neurons has yet to be demonstrated. Enkephalins are released from terminals of neostriatal-pallidal fibers but not from other efferent neurons of the striatum. Dopamine is released from the brainstem and some adjoining hypothalamic neurons but certainly not from striatal neurons. The neostriatum receives cortical inputs that utilize glutamate, but the release of GABA from terminals of striatal efferent fibers has not been demonstrated.

17- C
MPTP was discovered by accident when drug abusers who were using a synthetic heroin derivative developed signs of Parkinson's disease. It was discovered that their drug included the contaminant MPTP. As a consequence, MPTP has been applied systemically in a number of experimental animals, resulting in significant decreases in dopamine content of the brain due to the loss of dopaminergic neurons in the substantia nigra. These animals also developed symptoms similar to those seen in Parkinson's patients. For these reasons, this drug is currently being used for research purposes in order to develop a better understanding of this disease and to establish possible drug therapies for its treatment and eventual cure.

18- E
Since the flocculonodular lobe receives and integrates inputs from the vestibular system, it is understandable why lesions that disrupt this integrating mechanism for vestibular inputs would result in difficulties in maintaining balance. Indeed, this is a classic feature of lesions of the flocculonodular lobe but is not associated with lesions in the hemispheres of the posterior lobe, anterior limb of the internal capsule, or the dentate nucleus, which are functionally linked to the frontal lobe. Lesions of the anterior lobe also do not affect mechanisms of balance.

19- A
The centromedian nucleus is a classical nonspecific thalamic nucleus. It can modulate cortical activity by making local connections with specific thalamic nuclei, and therefore modify the specific thalamic inputs to different regions of the cerebral cortex. In addition, the centromedian nucleus also projects to the putamen. This projection is sometimes referred to as the thalamostriatal projection. Since the centromedian nucleus receives considerable inputs from the cerebral cortex, this connection to the putamen provides a basis by which the cerebral cortex can influence the basal ganglia in addition to its direct projections to the neostriatum.

20- E
The supraoptic nucleus, like the paraventricular nucleus, contains magnocellular neurons that synthesize vasopressin and oxytocin and transport these hormones down their axons to the posterior pituitary. For this reason, the supraoptic nucleus plays a significant role in the regulation of water balance. There is no evidence to support the notion that the supraoptic nucleus has a role in feeding behavior, temperature regulation, sexual behavior, or short-term memory functions.

21- D
Lesions of the lateral hypothalamus are likely to produce aphagia. Feeding behavior is elicited by stimulation of the lateral hypothalamus. Neurons in this region respond to the sight or taste of food. Since drinking is also associated with lateral hypothalamic functions, a lesion of this structure would also disrupt this behavior. Lesions of the lateral hypothalamus do not produce either hypertension or sexual behaviors. The neurons regulating these functions are elsewhere within the hypothalamus.

22- D
Recent studies have demonstrated that the suprachiasmatic nucleus controls the biologic clock of internal circadian rhythms. During the light phase of the light-dark cycle, metabolic activity (measured by 14C-2-deoxyglucose autoradiography) within the suprachiasmatic nucleus is significantly increased. In contrast, during the dark phase, there is very little metabolic activity.

23- A
The tumor is situated in the lentiform nucleus and internal capsule. Therefore, corticospinal fibers will be affected, causing a UMN paralysis of the left side. Dyskinesia would not be seen because any effects normally seen in association with damage to the basal ganglia would be masked by the effects of the damage to the internal capsule. Since the cerebellum was not involved, there would be no intention tremor. Neither would there be any visual deficits from this glioma since optic nerve fibers are not involved. The following schematic diagram indicates the approximate extent of the tumor. Labeled are the caudate nucleus (C), the globus pallidus (GP), the internal capsule (IC), the putamen (P), and the tumor (T).

24- C
This figure is a lateral view of the cerebral cortex. Cells in the "arm" area of the primary motor cortex (H) project their axons to the cervical level of the spinal cord. This area receives major input from the ventrolateral nucleus of the thalamus. The leg region of the primary somatosensory cortex (A) lies immediately caudal to the central sulcus, is almost devoid of pyramidal cells, and is referred to as a granulous cortex. Damage to the cells situated in the region of the dorsal border of the superior temporal gyrus and the adjoining area of the inferior parietal lobule (Wernicke's area) (C) causes impairment in the appreciation of the meanings of written or spoken words. 
    The primary, secondary, and tertiary auditory receiving areas in the cortex are located mainly in the superior temporal gyrus (D). It is the final receiving area for inputs from the medial geniculate nucleus, which represents an important relay in the transmission of auditory signals to the cortex. An additional area of the cortex governing speech (F) is called the motor speech area, or Broca's area. It is situated in the inferior aspect of the frontal lobe immediately rostral and slightly ventral to the precentral gyrus. Lesions of this region produce impairment of the ability to express words in a meaningful way or to use words correctly. The orbital frontal cortex (E) lies in a position inferior and rostral to Broca's motor speech area. This region governs higher-order intellectual functions and some aspects of emotional behavior. 
    The caudal aspect of the middle frontal gyrus (G) contains cells that, when activated, produce conjugate deviation of the eyes. This action is believed to be accomplished, in part, by virtue of descending projections to the superior colliculus, pretectal region, and horizontal gaze center of the pons. Lesions of the posterior parietal lobe (B) of the nondominant hemisphere will produce a disorder of body image, referred to as sensory neglect. The patient will frequently fail to recognize or neglect to shave or wash those body parts. The patient may even fail to recognize the presence of a hemiparesis involving that part of the body as well. The precentral gyrus (H) constitutes the primary motor cortex. Lesions of this region produce a UMN paralysis involving a contralateral limb.

25- 
1) A
There are three basic mechanisms by which the transmitter is removed from the synaptic cleft: (1) enzymatic degradation, (2) reuptake, and (3) diffusion. In the case of the neuromuscular junction, ACh (and not glutamate) is the neurotransmitter and the primary mechanism involves enzymatic degradation. The enzyme involved is acetylcholinesterase, which helps break down ACh into acetate and choline. Choline is then taken up by the presynaptic terminal. Concerning the other choices, choline acetyltransferase is the enzyme involved in the synthesis of ACh, glutaminase, and glutamine synthetase are involved in the formation of glutamate from glutamine and glutamine from glutamate, respectively. Serine hydroxymethyltransferase is the enzyme that converts serine into glycine.

2) D 
(see above explanation).

Sunday, June 30, 2013

Microbiology Self-Quiz (MCQs) with explanation

1. 
The latest and most effective therapy for AIDS patients includes azidothymidine (AZT), dideoxyinosine (DDI), and saquinavir or similar agents. Use of these three drugs would inhibit which of the following viral processes? 

A.   RNase, DNase
B. gp120 formation
C. p24 antibody expression
D. All membrane synthesis
E. Reverse transcriptase, protease

2.
A tube of monkey kidney cells is inoculated with nasopharyngeal secretions. During the next 7 days, no cytopathic effects (CPEs) are observed. On the eighth day, the tissue culture is infected accidentally with a picornavirus; nevertheless, the culture does not develop CPEs. Which of the following is the most likely explanation of this phenomenon?

A.   The nasopharyngeal secretions contained hemagglutinins
B. The nasopharyngeal secretions contained rubella virus
C. Picornavirus does not produce CPEs
D. Picornavirus does not replicate in monkey kidney cells
E. Monkey kidney cells are resistant to CPEs

3.
Which of the following is the most sensitive test for the diagnosis of herpes simplex (HSV) meningitis in a newborn infant?

A.   HSV IgG antibody
B. HSV polymerase chain reaction (PCR)
C. HSV culture
D. Tzanck smear
E. Cerebrospinal fluid (CSF) protein analysis

4.
One of the most common sexually transmitted diseases that may lead to cervical carcinoma is caused by which of the following viruses?

A.   Cytomegalovirus
B. Papillomavirus
C. Epstein-Barr virus
D. Herpes simplex virus
E. Adenovirus

5.
Meningitis is characterized by the acute onset of fever and stiff neck. Aseptic meningitis may be caused by a variety of microbial agents. During the initial 24 h of the course of aseptic meningitis, an affected person’s cerebrospinal fluid is characterized by which of the following?

A.   Decreased protein content
B. Elevated glucose concentration
C. Lymphocytosis
D. Polymorphonuclear leukocytosis
E. Eosinophilia

6.
Kuru is a fatal disease of certain New Guinea natives and is characterized by tremors and ataxia; Creutzfeldt-Jakob disease (CJD) is characterized by both ataxia and dementia. These diseases are thought to be caused by which of the following?

A.   Slow viruses
B. Cell wall–deficient bacteria
C. Environmental toxins
D. Prions
E. Flagellates

7.
An infant, seen in the ER, presents with a fever and persistent cough. Physical examination and a chest x-ray suggest pneumonia. Which of the following is most likely the cause of this infection?

A.   Rotavirus
B. Adenovirus
C. Coxsackievirus
D. Respiratory syncytial virus
E. Rhinovirus

8.
Which one of the following viruses may be human tumor virus? 

A.   Epstein-Barr virus (EBV)
B. HIV
C. Papillomavirus
D. Varicella-zoster virus (VZV)
E. Herpes simplex virus, type 2 (HSV)

9.
There is considerable overlap of signs and symptoms seen in congenital and perinatal infections. In a neonate with "classic" symptoms of congenital cytomegalovirus (CMV) infection, which one of the following tests would be most useful in establishing a diagnosis?

A.   CMV IgG titer on neonate’s serum at birth
B. CMV IgG titer on mother’s serum at birth of infant
C. CMV IgM titer on neonate’s serum at birth and at 1 month of age
D. Total IgM on neonate’s serum at birth
E. Culture of mother’s urine

10.
Interferon, a protein that inhibits viral replication, is produced by cells in tissue culture when the cells are stimulated with which of the following?

A.   Botulinum toxin
B. Synthetic polypeptides
C. Viruses
D. Chlamydiae
E. Gram-positive bacteria

11.
Which one of the following viruses would be most likely to establish a latent infection? 

A.   Adenovirus
B. Measles virus
C. Influenza virus
D. Parvovirus
E. Coxsackievirus group B

12.
Chicken pox is a common disease of childhood. It is caused by which of the following viruses? 

A.   Cytomegalovirus
B. Rotavirus
C. Varicella-zoster virus
D. Adenovirus
E. Papillomavirus

13.
Human warts are not only cosmetically unsightly but may lead to cancer of the cervix. They are caused by which one of the following viruses?

A.   Cytomegalovirus
B. Rotavirus
C. Varicella-zoster virus
D. Adenovirus
E. Papillomavirus

14.
A child has mononucleosis-like symptoms yet the test for mononucleosis and the EBV titers are negative. Which of the following is one cause of heterophile-negative mononucleosis?

A.   Cytomegalovirus
B. Herpes simplex virus
C. Varicella-zoster virus
D. Adenovirus
E. Coxsackievirus

15.
Malaise and fatigue with increased "atypical" lymphocytes and a reactive heterophil antibody test is most commonly caused by which of the following?

A.   Toxoplasma
B. Borrelia burgdorferi
C. Epstein-Barr virus
D. Parvovirus
E. Rubella virus

16.
Which of the following viruses causes progressive multifocal leukoencephalopathy (PML), a disease causing demyelination in the central nervous system?

A.   Human papillomavirus
B. West Nile virus
C. Tick-borne encephalitis virus
D. Polyomavirus
E. SSPE

17.
Which of the following is the leading cause of bronchiolitis and community-acquired pneumonia in infants?

A.   Measles virus
B. Influenza virus
C. Respiratory syncytial virus
D. Parainfluenza virus
E. Adenovirus

18.
A patient with a peptic ulcer was admitted to the hospital and a gastric biopsy was performed. The tissue was cultured on chocolate agar incubated in a microaerophilic environment at 37°C for 5 to 7 days. At 5 days of incubation, colonies appeared on the plate and were curved, Gram-negative rods, oxidase-positive. Which of the following is the most likely identity of this organism?

A.   Campylobacter jejuni
B. Vibrio parahaemolyticus
C. Haemophilus influenzae
D. Helicobacter pylori
E. Campylobacter fetus

19.
At a church supper in Nova Scotia, the following meal was served: baked beans, ham, coleslaw, eclairs, and coffee. Of the 30 people who attended, 4 senior citizens became ill in 3 days; 1 eventually died. Two weeks after attending the church supper, a 19-year-old girl gave birth to a baby who rapidly became ill with meningitis and died in 5 days. Epidemiologic investigation revealed the following percentages of people who consumed the various food items: baked beans, 30%; ham, 80%; coleslaw, 60%; eclairs, 100%; and coffee, 90%. Microbiologic analysis revealed no growth in the baked beans, ham, or coffee; many Gram-positive beta-hemolytic, short, rod-shaped bacteria in the coleslaw; and rare Gram-positive cocci in the eclairs. Which of the following is the most likely cause of this outbreak?

A.   Staphylococcus aureus
B. Listeria
C. Clostridium perfringens
D. Clostridium botulinum
E. Nonmicrobiologic

20.
Group B streptococcus sepsis in an infant is preventable. Which one of the following procedures is most likely to reduce the incidence of group B streptococcal disease?

A.   Intrapartum antibiotic treatment
B. Use of a polysaccharide vaccine
C. Screening of pregnant females in the last trimester
D. Identification of possible high-risk births
E. Screening of pregnant females at the first office visit, usually during the first trimester

21.
There has been much speculation on the pathogenesis of group B streptococcal disease in the neonate. Which of the following is the most likely pathogenic mechanisms?

A.   Complement C5a, a potent chemoattractant, activates PMNs
B. The streptococci are resistant to penicillin
C. The alternative complement pathway is activated
D. In the absence of specific antibody, opsonization, phagocyte recognition, and killing do not proceed normally

22.
A man who has a penile chancre appears in a hospital's emergency service. The VDRL test is negative. Which of the following is the most appropriate course of action?

A.   Send the patient home untreated
B. Repeat the VDRL test in 10 days
C. Perform dark-field microscopy for treponemes
D. Swab the chancre and culture on Thayer-Martin agar
E. Perform a Gram stain on the chancre fluid

23.
In people who have sickle cell anemia, osteomyelitis usually is associated with which of the following organisms?

A.   Micrococcus
B. Escherichia
C. Pseudomonas
D. Salmonella
E. Streptococcus

24.
A hyperemic edema of the larynx and epiglottis that rapidly leads to respiratory obstruction in young children is most likely to be caused by which of the following?

A.   K. pneumoniae
B. M. pneumoniae
C. Neisseria meningitidis
D. H. influenzae
E. H. hemolyticus

25.
A 70-year-old female patient was readmitted to a local hospital with fever and chills following cardiac surgery at a major teaching institution. Blood cultures were taken and a Gram-positive coccus grew from the blood cultures within 24 hours. Initial tests indicated that this isolate was resistant to penicillin.
Which of the following is the treatment of choice for the isolate? 

A.   Gentamicin
B. Gentamicin and ampicillin
C. Ciprofloxacin
D. Rifampin
E. No available treatment

26.
A 2-year-old infant is brought to the emergency room with hemolytic uremic syndrome and thrombocytopenia. Which one of the following bacteria would most likely be isolated from a stool specimen?

A.   Shigella
B. Salmonella
C. Aeromonas
D. E. coli 0157/H7
E. Enterobacter

27.
Which of the following is the most effective noninvasive test for the diagnosis of Helicobacter-associated gastric ulcers?

A.   Detection of H. pylori antigen in stool
B. Growth of H. pylori from a stomach biopsy
C. Growth of H. pylori in the stool
D. IgM antibodies to H. pylori
E. Culture of stomach contents for H. pylori

28.
A patient with symptoms of urinary tract infection had a culture taken, which grew 5 × 103 E. coli. The laboratory reported it as "insignificant." Which of the following is the most clinically appropriate action? 

A.   Do no further clinical workup
B. Suggest to the laboratory that low colony counts may reflect infection
C. Determine if fluorescent microscopy is available for the diagnosis of actinomycosis
D. Consider vancomycin as an alternative drug
E. Suggest a repeat antibiotic susceptibility test

29.
Which of the following is the antibiotic of choice for Lyme disease?

A.   Penicillin
B. Ampicillin
C. Erythromycin
D. Vancomycin
E. Ceftriaxone

30.
N. gonorrhoeae is a fastidious pathogen and found in sites often contaminated with normal flora. Which of the following is the best medium for isolation?

A.   Sheep blood agar
B. Löffler's medium
C. Thayer-Martin agar
D. Thiosulfate citrate bile salts sucrose medium
E. Löwenstein-Jensen medium

Answers

1- The answer is: E

The advent of triple therapy or a therapeutic "cocktail" has had a marked effect on AIDS patients. The combination of drugs work together as reverse transcriptive inhibitors and a protease inhibitor. Patients improve rapidly, their CD4 lymphocyte counts increase, and their HIV viral load is drastically reduced, often to <50 copies per ml. On the other hand, an untreated HIV-positive patient with a low CD4 and a high viral load (a) is at increased risk of opportunistic infection and (b) has a much greater chance of developing AIDS than if the viral load was <50,000. The patient is infectious and his HIV antibody screening test will be positive. The high viral load, however, is not a predictor of response to therapy. Many patients with high viral loads do very well on triple therapy, although resistance to one or more of the agents may subsequently occur. A low CD4 count does not predict progression to AIDS but does indicate increased chance of opportunistic infection such as those listed. Kaposi’s sarcoma, which has been linked to herpesvirus type 8, pneumocystis, and mycobacterial disease are three of the most prevalent opportunistic infections. While HIV-positive patients contract pneumococcal pneumonia, they are probably at no more risk than the general population, as protection against pneumococcal disease is linked to the presence of anticapsular antibody.

2- The answer is: B

Rubella virus does not produce cytopathic effects (CPEs) in tissue-culture cells. Moreover, rubella-infected cells challenged with a picornavirus are resistant to subsequent infection and thus would not exhibit CPEs. Monkey kidney cells infected only with picornavirus would show CPEs.

3- The answer is: B

HSV meningitis or encephalitis is difficult to diagnose by laboratory tests as there is a low titer of virus present in the CSF. Neonatal HSV infects the child during the birth process. While culture, Tzanck smear, and even antibody tests may be useful in adults, particularly those with HSV-rich lesions, they are not useful for CSF testing. Only PCR is sensitive enough to detect HSV DNA in the CSF. Once diagnosed rapidly, HSV encephalitis or meningitis can be treated with acyclovir.

4- The answer is: B

Human papillomavirus (HPV) is the cause of genital warts. It is one of the most pervasive of all the sexually transmitted diseases. There is no specific cure or vaccine. There are multiple serotypes of papillomavirus and some serotypes are linked to cervical cancer. New techniques for molecular diagnosis of HPV show promise for rapid and sensitive detection and perhaps more aggressive treatment.

5- The answer is: D

Aseptic meningitis is characterized by a pleocytosis of mononuclear cells in the cerebrospinal fluid; polymorphonuclear cells predominate during the first 24 h, but a shift to lymphocytes occurs thereafter. The cerebrospinal fluid of affected persons is free of culturable bacteria and contains normal glucose and slightly elevated protein levels. Peripheral white blood cell counts usually are normal. Although viruses are the most common cause of aseptic meningitis, spirochetes, chlamydiae, and other microorganisms also can produce the disease.

6- The answer is: D

Kuru and Creutzfeldt-Jakob disease (CJD) are similar but not identical diseases with very different epidemiology. Kuru is prevalent among certain tribes in New Guinea who practiced ritual cannibalism by eating the brains of the departed. CJD is found worldwide and has been transmitted by corneal transplants and in pituitary hormone preparations. There is some association between CJD and Mad Cow Disease in England. Prions are unconventional selfreplicating proteins, sometimes called amyloid. It is now thought that CJD, Kuru, and animal diseases such as scrapie, visna, and bovine spongiform encephalopathy (Mad Cow Disease) are caused by prions.

7- The answer is: D

Respiratory syncytial virus (RSV) is the most important cause of pneumonia and bronchiolitis in infants. The infection is localized to the respiratory tract. The virus can be detected rapidly by immunofluorescence on smears of respiratory epithelium. In older children, the infection resembles the common cold. Aerosolized ribavirin is recommended for severely ill hospitalized infants.

8- The answer is: C

Only two human viruses have been confirmed as human tumor viruses. They include human T-cell lymphoma/leukemia virus (HTLV) and papillomavirus. Others, such as EBV, HSV, and hepatitis B and C, have been implicated as tumor viruses. The virus that causes chicken pox (VZV) is not know to be oncogenic.

9- The answer is: C

(See figure below.) Presently, cytomegalovirus (CMV) is the most common cause of congenital and perinatal viral infections. Culture of the virus is a sensitive diagnostic technique; in the case of a neonate with classic symptoms, serum samples from the mother and neonate are obtained at birth. The IgM antibody titer in the infant’s serum should be higher than the mother’s titer, but they may be similar. For this reason, another sample from the infant at 1 month of age is tested simultaneously with the initial sample. The results should indicate a rise in IgM titer. Measurement of total IgM in the infant’s sera at birth is nonspecific and may show false-negative and false-positive reactions.
Cytomegalovirus-infected human embryonic fibroblasts stained with fluorescein-labeled monoclonal antibody to early nuclear antigen (×1000).

10- The answer is: C

Interferon is a protein that alters cell metabolism to inhibit viral replication. It induces the formation of a second protein that interferes with the translation of viral messenger RNA. Production of interferon has been demonstrated when cells in tissue culture are challenged with viruses, rickettsiae, endotoxin, or synthetic double-stranded polynucleotides. Interferon confers species-specific, not virus-specific, protection for cells.

11- The answer is: A

While the herpesviruses (HSV, CMV, VZV) are all well known for latency, adenovirus can also form a latent infection in the lymphoid tissue. In 50 to 80% of surgically removed tonsils or adenoids, adenovirus can be cultured. The virus has also been cultured from mesenteric lymph nodes, and, in rare cases, viral DNA has been detected in peripheral lymphocytes. Recurrent illness usually does not arise from these latent infections; however, activation can occur in the immunosuppressed.

12- The answer is: C

Varicella-zoster virus is a herpesvirus. Chicken pox is a highly contagious disease of childhood that occurs in the late winter and early spring. It is characterized by a generalized vesicular eruption with relatively insignificant systemic manifestations.
Adenovirus has been associated with adult respiratory disease among newly enlisted military troops. Crowded conditions and strenuous exercise may account for the severe infections seen in this otherwise healthy group.
Papillomavirus is one of two members of the family Papovaviridae, which includes viruses that produce human warts. These viruses are host-specific and produce benign epithelial tumors that vary in location and clinical appearance. The warts usually occur in children and young adults and are limited to the skin and mucous membranes.
Rotavirus is worldwide in distribution and has been implicated as the major etiologic agent of infantile gastroenteritis. Infection with this virus varies in its clinical presentation from asymptomatic infection to a relatively mild diarrhea to a severe and sometimes fatal dehydration. The exact mode of transmission of this infectious agent is not known. Because of severe side effects, the rotavirus vaccine has been recalled and is temporarily unavailable.
Infectious mononucleosis caused by cytomegalovirus (CMV) is clinically difficult to distinguish from that caused by Epstein-Barr virus. Lymphocytosis is usually present with an abundance of atypical lymphocytes. CMV-induced mononucleosis should be considered in any case of mononucleosis that is heterophil-negative and in patients with fever of unknown origin. 

13- The answer is: E

14- The answer is: A

Varicella-zoster virus is a herpesvirus. Chicken pox is a highly contagious disease of childhood that occurs in the late winter and early spring. It is characterized by a generalized vesicular eruption with relatively insignificant systemic manifestations.
Adenovirus has been associated with adult respiratory disease among newly enlisted military troops. Crowded conditions and strenuous exercise may account for the severe infections seen in this otherwise healthy group.
Papillomavirus is one of two members of the family Papovaviridae, which includes viruses that produce human warts. These viruses are host-specific and produce benign epithelial tumors that vary in location and clinical appearance. The warts usually occur in children and young adults and are limited to the skin and mucous membranes.
Rotavirus is worldwide in distribution and has been implicated as the major etiologic agent of infantile gastroenteritis. Infection with this virus varies in its clinical presentation from asymptomatic infection to a relatively mild diarrhea to a severe and sometimes fatal dehydration. The exact mode of transmission of this infectious agent is not known. Because of severe side effects, the rotavirus vaccine has been recalled and is temporarily unavailable.
Infectious mononucleosis caused by cytomegalovirus (CMV) is clinically difficult to distinguish from that caused by Epstein-Barr virus. Lymphocytosis is usually present with an abundance of atypical lymphocytes. CMV-induced mononucleosis should be considered in any case of mononucleosis that is heterophil-negative and in patients with fever of unknown origin. 

15- The answer is: C

Epstein-Barr virus (EBV) is a herpesvirus that causes a number of syndromes; the most common is infectious mononucleosis. It is a ubiquitous enveloped DNA virus. Only one serotype of EBV has been recognized, although molecular methods have reorganized a number of genotypes of EBV.
Infectious mononucleosis is an acute disease most commonly seen in younger people. It is characterized by a proliferation of lymphocytes, lymph node enlargement, pharyngitis, fatigue, and fever. Infection in young children is usually either asymptomatic or characteristic of an acute upper respiratory infection. Diagnosis is usually made by a positive heterophil test. Heterophil antibodies are those that occur in one species (human) and react with antigens of a different species. The heterophil test may be insensitive (30 to 60%) in children. Definitive diagnosis is made by detection of antibodies to EBV components.
EBV causes a variety of other syndromes including Burkitt’s lymphoma, the most common childhood cancer in Africa, and nasopharyngeal carcinoma, commonly seen in China.
Similar mononucleosis-like diseases are caused by cytomegalovirus (CMV) and Toxoplasma gondii, a parasite. CMV causes fewer than 10% of infectious mononucleosis-like diseases. CMV "mono" is primarily characterized by fatigue. Congenital infection with CMV almost always causes serious sequelae, such as retardation and hearing loss. T. gondii also causes a variety of clinical problems, among them encephalitis in AIDS patients and food poisoning from the ingestion of raw meat. Although CMV and T. gondii are relatively rare causes of infectious mononucleosis, they must be ruled out, particularly when EBV tests are nonreactive.

16- The answer is: D

Human papillomaviruses (HPV) are the causative agents of cutaneous warts as well as proliferative squamous lesions of mucosal surfaces. Although most infections by human papillomavirus are benign, some undergo malignant transformation into in situ and invasive squamous cell carcinoma. Both HPV and polyomavirus have icosahedral capsids and DNA genomes. JC virus, a polyomavirus, was first isolated from the diseased brain of a patient with Hodgkin’s lymphoma who was dying of progressive multifocal leukoencephalopathy (PML). This demyelinating disease occurs usually in immunosuppressed persons and is the result of oligodendrocyte infection by JC virus. JC virus has also been isolated from the urine of patients suffering from demyelinating disease. Cryotherapy and laser treatment are the most popular therapies for warts, although surgery may be indicated in some cases. At the present time, there is no effective antiviral therapy for treatment of infection with polyomavirus or HPV. West Nile virus is an arbovirus. While prevalent in Europe, Africa, and the Middle East, it was not seen in the United States until the summer of 1999. It is transmitted by mosqitoes and birds, especially crows; these animals are a reservoir. WNV causes a rather mild encephalitis in humans, the exception being older patients or those who may be immunocompromised.

17- The answer is: C

Orthomyxoviruses and paramyxoviruses are RNA viruses that contain a single-stranded RNA genome. The influenza viruses belong to the orthomyxoviruses. They cause acute respiratory tract infections that usually occur in epidemics. Isolated strains of influenza virus are named after the virus type (influenza A, B, or C) as well as the host and location of initial isolation, the year of isolation, and the antigenic designation of the hemagglutinin and neuraminidase. Both the hemagglutinin and neuraminidase are glycoproteins under separate genetic control, and because of this they can and do vary independently. The changes in these antigens are responsible for the antigenic drift characteristic of these viruses. The paramyxoviruses include several important human pathogens (mumps virus, measles virus, respiratory syncytial virus, and parainfluenza virus). Both paramyxoviruses and orthomyxoviruses possess an RNA-dependent RNA polymerase that is a structural component of the virion and produces the initial RNA. Respiratory syncytial viruses (RSV) are not related to the paramyxoviruses. They are 150-nm single-stranded RNA viruses. There are 2 antigen groups, A and B, which play no role in diagnosis and treatment. While the overall mortality is 0.5%, at-risk groups may be 25 to 35% mortality if untreated. Some parainfluenza virus infections (type 3) may be indistinguishable from RSV, but most parainfluenza infections produce a laryngotracheobronchitis known as croup.

18- The answer is: D

Helicobacter pylori was first recognized as a possible cause of gastritis and peptic ulcer by Marshall and Warren in 1984. This organism is readily isolated from gastric biopsies but not from stomach contents. It is similar to Campylobacter species and grows on chocolate agar at 37°C in the same microaerophilic environment suitable for C. jejuni (Campy-Pak or anaerobic jar [Gas Pak] without the catalyst). H. pylori, however, grows more slowly than C. jejuni, requiring 5 to 7 days incubation. C. jejuni grows optimally at  42°C, not 37°C, as does H. pylori.

19- The answer is: E

There have been a number of outbreaks of food poisoning caused by Listeria monocytogenes. Listeria is a common inhabitant of farm animals and can be readily isolated from silage, hay, and barnyard soil. Humans at the extremes of age are most susceptible to Listeria infection but only recently has food been implicated as a vehicle. In the outbreak in Nova Scotia, it is likely that the cabbage used for the coleslaw was fertilized with animal droppings and not properly washed prior to consumption. Major Listeria outbreaks associated with cheese have been seen in the United States and most likely have originated from contaminated milk. Epidemiologic investigation often will provide data on attack rates in such outbreaks. The eventual solution of the problem always lies in a combination of epidemiologic, microbiologic, and clinical information. For example, in the Nova Scotia case, it should not be assumed that the eclairs were the culprit based on the fact that everyone ate them.

20- The answer is: A

The incidence of group B streptococcal disease (GBS) is 1–3 cases per 1000 births. Neonates acquire the disease during birth from mothers who harbor the organism. Risk factors include prematurity, premature rupture of membranes, and group B streptococcal carriage. The Gram's stain of cerebrospinal fluid is a rapid test for GBS disease. Although sensitive, the Gram's stain requires experience to differentiate these streptococci from other Gram-positive cocci. Latex tests for GBS antigen are also available, but sensitivity in CSF is not significantly higher than the Gram's stain. GBS can be reduced by intrapartum administration of penicillin. Experimentally, GBS polysaccharide vaccines have also been used. Screening pregnant females early in pregnancy probably offers little advantage because of the possible acquisition of GBS late in the pregnancy. There has been speculation concerning the pathogenesis of GBS. These include failure to activate complement pathways and immobilization of polymorphonuclear leukocytes (PMNs) due to the inactivation of complement C5A, a potent chemoattractant. While GBS is relatively more resistant to penicillin than group A streptococci, the great majority of GBS isolates are still penicillin-susceptible. An aminoglycoside such as gentamicin may be added to GBS treatment regimens due to the relative reduced susceptibility of some strains.

21- The answer is: D

The incidence of group B streptococcal disease (GBS) is 1–3 cases per 1000 births. Neonates acquire the disease during birth from mothers who harbor the organism. Risk factors include prematurity, premature rupture of membranes, and group B streptococcal carriage. The Gram's stain of cerebrospinal fluid is a rapid test for GBS disease. Although sensitive, the Gram's stain requires experience to differentiate these streptococci from other Gram-positive cocci. Latex tests for GBS antigen are also available, but sensitivity in CSF is not significantly higher than the Gram's stain. GBS can be reduced by intrapartum administration of penicillin. Experimentally, GBS polysaccharide vaccines have also been used. Screening pregnant females early in pregnancy probably offers little advantage because of the possible acquisition of GBS late in the pregnancy. There has been speculation concerning the pathogenesis of GBS. These include failure to activate complement pathways and immobilization of polymorphonuclear leukocytes (PMNs) due to the inactivation of complement C5A, a potent chemoattractant. While GBS is relatively more resistant to penicillin than group A streptococci, the great majority of GBS isolates are still penicillin-susceptible. An aminoglycoside such as gentamicin may be added to GBS treatment regimens due to the relative reduced susceptibility of some strains.

22- The answer is: C

In men, the appearance of a hard chancre on the penis characteristically indicates syphilis. Even though the chancre does not appear until the infection is 2 or more weeks old, the VDRL test for syphilis still can be negative despite the presence of a chancre (the VDRL test may not become positive for 2 or 3 weeks after initial infection). However, a lesion suspected of being a primary syphilitic ulcer should be examined by dark-field microscopy, which can reveal motile treponemes.

23- The answer is: D

Many types of infection, notably respiratory tract infections and osteomyelitis, are common in people who have sickle cell anemia. For unknown reasons, Salmonella is implicated frequently in these infections. Osteomyelitis in other persons is caused most often by Staphylococcus.

24- The answer is: D

Haemophilus influenzae is a Gram-negative bacillus. In young children, it can cause pneumonitis, sinusitis, otitis, and meningitis. Occasionally, it produces a fulminative laryngotracheitis with such severe swelling of the epiglottis that tracheostomy becomes necessary. Clinical infections with this organism after the age of 3 years are less frequent.

25- The answer is: E

Enterococci causes a wide variety of infections ranging from less serious, for example, urinary tract infections, to very serious, such as septicemia. A Gram-positive coccus resistant to penicillin must be assumed to be enterococcus until other more definitive biochemical testing places the isolate in one of the more esoteric groups of Gram-positive cocci. Once isolated, there are a variety of tests to speciate enterococci. However, penicillin-resistant, non--lactamase-producing, vancomycin-resistant, Gram-positive cocci are most likely Enterococcus faecium. There are a variety of mechanisms for vancomycin resistance in E. faecium and they have been termed Van A, B, or C. These isolates have become one of the most feared nosocomial pathogens in the hospital environment. Unfortunately, no approved antibiotics can successfully treat vancomycin-resistant enterococci (VRE), only some experimental antibiotics such as Synercid.

26- The answer is: D

Food poisoning with E. coli 0157/H7 causes hemorrhagic colitis; it is often seen after eating beef hamburgers. The same organism also causes a hemorrhagic uremic syndrome. The toxin, called Shiga-like toxin, can be demonstrated in Vero cells, but the cytotoxicity must be neutralized with specific antiserum. With the exception of sorbitol fermentation, there is nothing biochemically distinctive about these organisms.

27- The answer is: A

H. pylori antigen tests using an ELISA format and a monoclonal antibody to H. pylori are as sensitive as culture of the control portion of the stomach. Urea breath tests are also widely used. H. pylori has an active enzyme (urease) which breaks down radioactive urea. The patient releases radioactive CO2 if H. pylori are present. H. pylori antibody tests, IgG and IgA, indicate the presence of H. pylori and usually decline after effective treatment. Culture of stomach contents is insensitive and not appropriate as a diagnostic procedure for H. pylori. Direct tests such as antigen or culture of gastric mucosa are preferred because they are the most sensitive indication of a cure.

28- The answer is: B

This question demonstrates a commonly occurring clinical infectious disease and microbiologic problem. Enterococci may be resistant to ampicillin and gentamicin. Vancomycin would be the drug of choice. However, laboratory results do not always correlate well with clinical response. The National Committee on Clinical Laboratory Standards recommends testing enterococci only for ampicillin and vancomycin.
Some symptomatic patients may have 10 leukocytes per mL of urine but relatively few bacteria. The patient is likely infected and the organisms, particularly if in pure culture, should be further processed.

29- The answer is: E

There are few bacteria for which antimicrobial susceptibility is highly predictable. However, some agents are the drug of choice because of their relative effectiveness. Among the three antibiotics that have been shown to treat legionellosis effectively (erythromycin, rifampin, and minocycline), erythromycin is clearly superior, even though in vitro studies show the organism to be susceptible to other antibiotics.
Penicillin remains the drug of choice for S. pneumoniae and the group A streptococci, although a few isolates of penicillin-resistant pneumococci have been observed. Resistance among the pneumococci is either chromosomally mediated, in which case the minimal inhibitory concentrations (MICs) are relatively low, or plasmid-mediated, which results in highly resistant bacteria. The same is generally true for H. influenzae. Until the mid-1970s, virtually all isolates of H. influenzae were susceptible to ampicillin. There has been a rapidly increasing incidence of ampicillin-resistant isolates, almost 35 to 40% in some areas of the United States. Resistance is ordinarily mediated by -lactamase, although ampicillin-resistant, -lactamase-negative isolates have been seen. No resistance to penicillin has been seen in group A streptococci.
C. difficile causes toxin-mediated pseudomembranous enterocolitis as well as antibiotic-associated diarrhea. Pseudomembranous enterocolitis is normally seen during or after administration of antibiotics. One of the few agents effective against C. difficile is vancomycin. Alternatively, bacitracin can be used.


Lyme disease, caused by B. burgdorferi, has been treated with penicillin, erythromycin, and tetracycline. Treatment failures have been observed. Ceftriaxone has become the drug of choice, particularly in the advanced stages of Lyme disease. 

30- The answer is: C

The medium of choice for the isolation of pathogenic neisseriae is Thayer-Martin (TM) agar. TM agar is both a selective and an enriched medium; it contains hemoglobin, the supplement Isovitalex, and the antibiotics vancomycin, colistin, nystatin, and trimethoprim.
V. cholerae as well as other vibrios, including V. parahaemolyticus and V. alginolyticus, are isolated best on thiosulfate citrate bile salts sucrose medium, although media such as mannitol salt agar also support the growth of vibrios. Maximal growth occurs at a pH of 8.5 to 9.5 and at 37°C incubation.
 Löwenstein-Jensen slants or plates, which are composed of a nutrient base and egg yolk, are used routinely for the initial isolation of mycobacteria. Small inocula of M. tuberculosis can also be grown in oleic acid albumin media; large inocula can be cultured on simple synthetic media.
Löffler's medium, which is very rich, supports the growth of C. diphtheriae but suppresses the growth of most other nasopharyngeal microflora. C. diphtheriae colonies on this medium appear small, gray, and granular and have uneven edges.
S. aureus grows very well on sheep blood agar, which is made up of a nutrient base and 5 to 8% sheep blood; selective and differential media, such as mannitol salt agar, also are available for S. aureus.