1. _____ A
7-year-old patient presents with pain in the left ear. Pus is drained from the
ear and a sample sent for culture. Gram stain reveals neutrophils and small
Gram-negative bacteria. A common pathogen in this setting is Haemophilus
influenzae. However, the bacteria in the smear are so small that it is
difficult to decide whether they are really rods or cocci. What information
from the lab would allow identification of the organism as H. influenzae?
A. Growth
on chocolate agar in elevated CO2 but not room air.
B.
β-hemolysis around colonies on sheep blood agar.
C. Ability
to grow in medium containing 6.5% NaCl.
D.
Sensitivity to bacitracin and resistance to optochin.
E. Positive
bile-esculin test.
F. Growth on broth-based agar supplemented with
hemin and NAD
(= Factors X and V).
2. _____
Successful immunization against Tetanus results in production of antibodies
that prevent disease.
By what
mechanism do these protective antibodies prevent Tetanus?
A. Opsonize
cells of C. tetani.
B. Prevent
binding of C. tetani endotoxin to monocyte receptors.
C. Bind C.
tetani flagella, prevent cell motility and access to neurons.
D. Bind C.
tetani cells and activate complement.
E. Bind
toxin receptors on neuron plasma membranes, prevent binding/entry of toxin.
F. Neutralize the protein exotoxin of C.
tetani.
3. _____ A
15-year-old male from west-central New Jersey has been ill for five days with
fever, chills, and headache, and today woke to find a rash covering his body
and limbs, including his palms and soles.
The rash is
composed of fine macular lesions (macule = flat spot, red but not raised).
Rocky Mountain
Spotted
Fever should be high on your list of possible causes. To help confirm or rule
out this possibility, you need to ask him about possible exposure to the source
of this disease.
What should
you ask him about?
A. Drinking
un-chlorinated water.
B. Eating
raw meat.
C.
Unprotected sex.
D. Tick bites.
E. Contact
with pet reptiles or birds.
Questions 4-6: An elderly man with a
post-surgical infection.
An
intravenous catheter was put in place for delivery of antibiotics and other
medications. He developed fever and pneumonia 3 days after surgery. Sputum
culture on sheep blood agar grew out numerous small gray α- hemolytic colonies;
about 10% of colonies were larger, white, shiny, opaque, and β-hemolytic. Only
the latter type grew from blood cultures. Both colony types contained
Gram-positive cocci. The lab reported the small colonies as ‘oral streptococci’
and the larger colonies as ‘coagulase-negative Staphylococci’.
4. _____
What test was used to distinguish Staphylococci from Streptococci?
A. Catalase test
B.
Coagulase test
C. Oxidase
test
D.
Sensitivity to optochin
E.
Sensitivity to bacitracin
F. CAMP
test
5. _____
What does the coagulase-negative result indicate?
A. The
organism is more virulent than other staphylococci.
B. The
organism is likely to produce a superantigen toxin.
C. The
patient is in little or no danger of developing septic shock.
D. The
Gram-positive staining was likely the result of improper laboratory procedure.
E. The catheter entry site is likely to have
been infected by normal skin flora.
6. _____ An
important virulence factor of coagulase-positive staphylococci is Protein A.
How does
Protein A aid in virulence?
A. Binds the Fc region of IgG, decreases
opsonization.
B.
Hydrolyzes secretory IgA.
C. Binds
Factor H, prevents activation of complement.
D. Extracts
iron from plasma proteins.
E. Promotes
tight binding of bacteria to extracellular matrix.
Questions 7-9: An HIV-positive patient with
hemoptysis.
He is 30
years old and has been referred to you because of hemoptysis (= coughing up
blood). A cavitary lesion in the right upper lobe of the lung is seen on chest
x-ray (Cavitary lesion = opaque lesion on x-ray with a central region of low
density produced by death of tissue.) A sample of sputum is obtained and a
smear is acid-fast-stained using the red dye carbol-fuchsin.
7. _____ If
this is tuberculosis, what would you expect to observe after acid-fast stain of
sputum?
A. No
stained bacteria
B. Irregularly-staining
red branching filaments.
C. Red
acid-fast cocci, in grape-like clusters
D.
Blue-staining bacilli.
E. Red-staining bacilli.
8. _____
The patient is given a tuberculin test. Three days later, there is induration
and erythema, 32 mm in diameter, at the site of injection, a positive test
result.
What
process produced the induration and erythema?
A.
Activation of complement.
B.
Induction of a primary antibody response.
C. Invasion
and lysis of epithelial cells by bacteria.
D. Cytokine production by CD4+ T lymphocytes.
E. Release
of inflammatory cell-envelope components from bacteria.
9.______
The sputum sample was sent for culture on Lowenstein-Jensen agar and in the
BACTEC system.
The
probable diagnosis was readily established by x-ray, direct smear, and skin
testing.
Why was the
labor- and time-intensive culture procedure performed?
A. Many
fungi stain acid-fast.
B. Only
highly-virulent mycobacteria grow on the media used for culture.
C. Culture allows testing for antibiotic
sensitivity/resistance.
D. Rapid
growth of mycobacteria correlates with high virulence.
Choose the
single best answer to each question.
10. _____
Streptococcus pneumoniae, Haemophilus influenzae, Neisseria meningitidis, and
Cryptococcus neoformans all colonize the upper respiratory tract and can spread
from there to the meninges. What essential virulence factor, that aids
meningeal spread, is produced by all four organisms?
A. IgA
protease
B. Polysaccharide capsule
C. Thick
peptidoglycan
D.
Endotoxin
E. Exotoxin
11. _____
Seven children in a third-grade class developed bloody diarrhea; one of them
was hospitalized with renal failure. Stool cultures for Gram-positive and
Gram-negative bacteria (including Campylobacter) yielded only “normal
intestinal flora” and “lactose-positive organisms” on MacConkey agar.
Epidemiologists found that, three days before the outbreak, the class had gone
to a local restaurant for a party. All children who became ill, and none who
did not, had eaten hamburgers. Later it was found that some lactose fermenters
failed to ferment sorbitol. Which organism is most strongly suggested by the
laboratory and epidemiologic data?
A. Bacillus
cereus
B.
Campylobacter jejuni
C.
Clostridium perfringens
D. Escherichia coli
E. Listeria
monocytogenes
F.
Salmonella enterica
G.
Staphylococcus aureus
H. Yersinia
enterocolitica
12._____ An
18-year-old man is seen in clinic for urethral discharge. Gram-stained smear of
exudate contains neutrophils and Gram-negative diplococci, many of them
intracellular. He is treated with ceftriaxone (a β-lactam) but does not get
better, and returns. On his second visit, Gram-stained smear of exudate
contains neutrophils but no bacteria are visible, and culture of exudate
produces no colonies on Sheep blood, Chocolate, or Thayer-Martin agars in
elevated CO2.
Which two
species below are most likely to have caused his infections?
A.
Klebsiella pneumoniae and Chlamydia pneumoniae
B.
Neisseria meningitidis and Chlamydia trachomatis
C.
Legionella pneumophila and Mycoplasma pneumoniae
D.
Treponema pallidum and Ehrlichia phagocytophila
E. Neisseria gonorrhoeae and Mycoplasma
hominis
Questions 13-15: A young woman with a
post-chemotherapy infection.
A
21-year-old woman with leukemia was treated with a brief intensive course of
cytotoxic drugs. Ten days after therapy began she developed fever and shortness
of breath. A CBC (complete blood count) showed her to be highly neutropenic.
Chest x-ray revealed a dense lesion in her left lung. Sputum culture grew out
“normal oral flora” plus large fuzzy colonies. Under the microscope the fuzzy
colonies contained hyphae (with septa) which branched at acute angles, and
conidia in chains. In a silver-stained biopsy of the lung lesion branching
hyphae were seen in tissue.
13. _____
What process is most likely to have created the patient’s neutropenia?
A. Cytokine
production by leukemic cells.
B. Killing of dividing cells by cytotoxic
anti-cancer drugs.
C. Killing
by toxins secreted by the pathogen.
D.
Induction of apoptosis by the pathogen.
E. A
genetic defect in neutrophil production.
14. _____
To what genus is the pathogen most likely to belong?
A.
Actinomyces
B. Aspergillus
C.
Klebsiella
D.
Mycobacterium
E.
Mycoplasma
F. Mucor
G.
Pneumocystis
H.
Staphylococcus
I.
Streptococcus
J. Rhizopus
15. _____
With what drug should the patient be treated?
A. Another
β-lactam
B. A β-lactam
plus an aminoglycoside
C. An
aminoglycoside alone
D. An azole
E. A
tetracycline
16. _____
Gastroscopy reveals that a patient with stomach pain has a large ulceration of
his gastric mucosa. During the procedure a biopsy of the stomach epithelium is
obtained.
Which
observation would suggest Helicobacter pylori as the cause of illness?
A. Curved or spiral bacteria seen in the
biopsy after silver staining.
B. Biopsy
shows infiltration of gastric epithelium by lymphocytes.
C. pH of
stomach fluid is equal to 1 (normal), rather than decreased.
D. Ingested
isotope-labeled nitrate is converted to nitrite in the stomach.
E. Bacteria
are found in stomach fluid, but not in contact with the gastric epithelium.
17. _____ A
75-year-old man reports malaise, headache, and fever. On examination his neck
is mildly stiff. Gram stain of the patient's CSF reveals neutrophils and
numerous Gram-negative cocci, many in pairs. Which organism below is most
likely?
•
Pseudomonas aeruginosa
•
Klebsiella pneumoniae
•
Haemophilus influenzae
•
Escherichia coli
•
Treponema pallidum
•
Nocardia asteroides
•
Neisseria gonorrhoeae
•
Neisseria
meningitides
18. _____ A
young man develops peritonitis following abdominal trauma. During surgery
foul-smelling purulent material is aspirated from the infected area. Gram stain
of this material contains a mixture of Gram positive cocci, Gram-positive rods,
and many Gram-negative rods. Aerobic culture on sheep blood agar yields many
colonies of enterococci and a few colonies of E. coli; culture on MacConkey
agar produces only sparse colonies of E. coli. Anaerobic culture on sheep blood
agar produces a few colonies of β-hemolytic Gram-positive rods and many
colonies of slender Gram-negative rods.
Which
organism is most likely to represent the majority of the Gram-negative rods
seen when peritoneal exudate was stained?
•
Yersinia enterocolitica
•
Clostridium perfringens
•
Clostridium tetani
•
Pseudomonas aeruginosa
•
Salmonella typhi
•
Yersinia pseudotuberculosis
•
Bacteroides
fragilis
Questions 19-20: A woman with neurological
illness.
19. _____ A
55-year-old woman develops diplopia, one day after eating home-canned fruit.
(Diplopia = double vision, from inability to coordinate the direction of gaze
of the eyes.) A few hours later she develops difficulty speaking, bilateral
weakness of her arms, nausea, vomiting, dizziness, blurred vision, and dry
mouth. However she is alert, oriented, and has no fever.
If this is
botulism, by what mechanism did Clostridium botulinum produce her signs and
symptoms?
A. Bound to
Toll-like receptors and stimulated production of inflammatory cytokines.
B. Injected
proteins into neurons via a type III secretion system.
C. Secreted a protein toxin that enters
mammalian neurons and blocks synaptic transmission.
D. Released
peptidoglycan and other inflammatory components of the cell envelope.
E.
Bacteremic spread followed by infection of multiple tissues: eyes, muscle,
stomach, nervous system, salivary glands.
20. _____
Home-canned food is a common source of botulism in adults. What property of C.
botulinum facilitates infection by this route?
A. Produces airborne spores not easily killed
by boiling.
B.
Vegetative cells grow best at cooking temperatures.
C.
Extremely resistant to gastric acid.
D. Thick
peptidoglycan renders cells resistant to heat, cold, and drying.
E. Surface
proteins inhibit digestive hydrolases.
Questions 21-23: Gram-positive septicemia.
A
25-year-old man has high fever and elevated white count. Blood cultures are
obtained. He is treated with a broad spectrum cephalosporin plus an
aminoglycoside. The next day the laboratory reports that cultures contain
catalase positive Gram-positive cocci in clusters. Identification of the
organism and determination of antibiotic sensitivity are underway. Pending
arrival of these results, the cephalosporin is replaced with vancomycin.
21. _____
What was the major rationale for this change?
A.
Cephalosporins (as a class) have a narrower spectrum of action than vancomycin.
B. The lab results suggest staphylococci,
many of which are resistant to cephalosporins.
C. Lysis of
bacteria by cephalosporins may result in a massive inflammatory reaction.
D.
Vancomycin is a bactericidal antibiotic whereas cephalosporins are only
bacteriostatic.
The
organism is identified as Staphylococcus aureus.
Antibiotic
sensitivity testing results are as follows:
Penicillin
G R
Oxacillin
(anti-staph penicillin) R
Third-generation
cephalosporin R
Vancomycin s
Erythromycin
(macrolide) R
Tobramycin
(aminoglycoside) R
Chloramphenicol R
Trimethoprim/sulfa
(metabolic
inhibitor) s
22. ____
What is the most likely genetic/biochemical basis of this isolate’s resistance
to oxacillin and the cephalosporin?
A. Small
non-conjugative plasmid that encodes a penicillinase.
B.
Conjugative plasmid, contains transposon that encodes a broad-spectrum
β-lactamase.
C. DNA insert into chromosome, encodes a
‘penicillin-binding protein’ (= peptidoglycan cross-linking enzyme) resistant
to β-lactams.
D. There is
no D-ala-D-ala in the side chains of peptidoglycan.
E. No
peptidoglycan is present in the cell wall.
23. ______
What essential process in Staphylococcus aureus is inhibited by Erythromycin?
A.
Methylation of ribosomal RNA.
B.
Production of DNA supercoils by Topoisomerase II
C.
Cross-linking of peptidoglycan chains by transpeptidases.
D.
Enzymatic activity of dihydrofolate reductase.
E. Peptide bond formation by bacterial
ribosomes.
24. _____ A
security guard at a New Jersey Court House comes to your office with a large
lesion on his left arm. It is 10 cm in diameter and ulcerated. Surrounding
tissue is red and markedly swollen. The ulcer is healing to produce a black
scab. A swab of the ulcer contains large Gram-positive rods. After aerobic
culture on sheep blood agar these produce large β-hemolytic colonies.
Which
organism is most likely?
A. Bacillus anthracis
B. Bacillus
cereus
C.
Clostridium difficile
D.
Clostridium perfingens
E.
Clostridium tetani
F. Listeria
monocytogenes
25._____ A
25-year-old medical student returns to New Jersey from Spring Break (which he
spent fishing in North Carolina). Soon afterwards, he becomes ill. He reports a
5-day history of fever, malaise, and headache. He has three “Bull’s eye”
lesions on his thighs. Lesions are 10-15 cm in diameter, oval with somewhat
irregular outlines, with 3-4 cm red borders and 2-4 cm central red areas, separated
by a belt of paler skin. Which diagnosis is most likely?
•
A dermatophyte such as Trichophyton
•
Babesiosis
•
Lyme disease
•
Relapsing fever
•
Rocky Mountain spotted fever
•
Staphylococcal scalded skin syndrome
•
Primary syphilis
•
Secondary syphilis
26. _____ A
12-year-old girl presents with fever, malaise, and a red, painful, swollen,
right hand and prominent lymphadenopathy of the arm and axilla. The patient has
a cat and reports that a few days ago the wretched ungrateful creature bit her
on the right hand.
What
pathogen is most strongly suggested by the history?
•
An alpha-hemolytic Streptococcus
•
Bartonella (=Rochalimea) henselae
•
Brucella abortus
•
Ehrlichia canis
•
Francisella tularanesis
•
Legionella pneumophila
•
Pasteurella
multocida
•
Yersinia pestis
•
Questions 27-29: A young woman with an abscess.
A
23-year-old female college student went to the Student Health Service because
of fever, myalgia, and a five-cm abscess: hot, red, swollen, and painful, with
a ‘head’ of pus forming. This was lanced, drained, and disinfected. She was
given antibiotics and acetaminophen (Tylenol). Late that day her roommate found
her disoriented and took her to the Emergency Room. Her blood pressure was
below normal and her pulse elevated. She showed no signs of meningitis but was
lethargic and reported severe muscle aches. She was admitted. The next morning
she was still hypotensive and showed signs of liver (jaundice) and kidney (poor
urine output) dysfunction. Blood levels of liver and muscle enzymes were
elevated. The preliminary diagnosis was Toxic Shock Syndrome.
27. _____
What process damaged liver, kidney, and muscle?
A. Bacteria
infected these sites by gaining access to the bloodstream from the abscess.
B. A
bacterial exotoxin acted on the central nervous system; organ damage was a
secondary result.
C.
Lipopolysaccharide released from dying bacteria caused monocytes to produce
inflammatory cytokines.
D. A bacterial exotoxin stimulated production
of toxic levels of inflammatory cytokines by T cells.
E. Bacteria
bound to plasma membrane receptors of nerve, muscle, and kidney, and induced
apoptosis.
28. _____
In a stained smear of pus from the abscess, what cell type would you expect to
predominate?
A.
Basophils
B.
Eosinophils
C. Neutrophils
D.
Lymphocytes
E.
Monocytes
29. _____
What process was most largely responsible for the swelling around the abscess?
A. Dilation
of small blood vessels
B. Increase in permeability of small blood
vessels
C.
Increased responsiveness of local sensory nerve endings
D.
Proliferation of fibroblasts
E.
Infiltration of tissue by inflammatory cells
30. _____ A
medical student doing research accidentally stabs himself in the left wrist
with a needle containing purified E. coli outer membranes. Two hours later he
arrives at the Emergency Room with a red, swollen wrist and a fever of 40oC.
What
process would you expect to have been most effective in producing his fever?
A. Binding
of O-antigen by IgG antibodies
B. Binding of Toll-like Receptors by Lipid A
C. Binding
of magnesium ions by core polysaccharide
D. Binding
of peptidoglycan to macrophage ‘scavenger receptors’
E. Binding
of porin proteins by siderophores.
31. _____ A
patient presented with upper back pain. MRI imaging demonstrated inflammation
of the T8-T9 vertebral bodies consistent with osteomyelitis. A bone marrow
biopsy, when cultured, produced colonies of Gram-positive cocci. Colonies on
Sheep blood agar were 3-4 mm in diameter, off-white and beta-hemolytic.
Colonies on Brain-heart infusion (BHI) agar were 2-3 mm in diameter and golden
yellow.
Catalase
and coagulase tests were positive.
What is the
most likely pathogen?
•
Streptococcus pyogenes
•
Streptococcus pneumoniae
•
Streptococcus mitis (or a related ‘oral streptococcus’)
•
Streptococcus agalactiae
•
Staphylococcus epidermidis (or a related skin organism)
•
Staphylococcus
aureus
32. _____
Gram stain of material aspirated from a subcutaneous abscess contained huge
numbers of neutrophils and clusters of branched, weakly-staining, Gram-positive
filaments. The filaments were also weakly acid-fast. The organisms grew in
aerobic culture.
What
organism is most likely?
A.
Actinomyces israelii
B. Nocardia asteroides
C.
Sporothrix schenckii
D. An
‘environmental mycobacterium’
E.
Corynebacterium diphtheriae
F. Bacillus
cereus
33. _____ A
food-borne outbreak of Salmonella enteritis takes place in central New Jersey
and is traced to chicken parts sold by a supermarket chain. Isolates from all
cases are of serotype O104:H6.
What
bacterial structures correspond to “O” and “H” antigens?
O-Antigen:
H-antigen:
A. Carbohydrate chains of LPS
Flagella
B.
Polysaccharide capsule
Common or adhesive pili
C. Porins
of outer membrane
Conjugation pili
D. Peptide
chains of peptidoglycan Non-pilus
surface adhesins
E.
Fibrillar proteins
Teichoic acids of cell envelope
34. _____ A
24-year-old man comes to clinic with a severely swollen, red, and painful
pharynx. A Gram-stained smear of exudate contains abundant neutrophils and
slender Gram-negative rods. A sample is sent for culture and he is treated with
a broad-spectrum antibiotic. The Gram-negative rod grows on Chocolate agar but
not on standard Sheep blood agar when plates are cultured in room air.
Which of
the following organisms is most likely?
A.
Bordetella pertussis
B.
Chlamydia pneumoniae
C. Haemophilus influenzae
D.
Klebsiella pneumoniae
E.
Legionella pneumophila
35. ____
Isolates of Neisseria meningitidis that cause septicemia/meningitis produce
capsules. Isolates which produce less-serious disease usually lack capsules.
Infection with non-encapsulated isolates results in protective immunity to
them. The antibodies usually bind to bacterial surface proteins.
In the
genesis of these protective antibodies, which of the following is essential?
A. B
lymphocytes are stimulated in a “T-independent” fashion.
B. CD8+
lymphocytes proliferate.
C.
Neutrophils process and present bacterial antigen to T cells.
D. Dendritic cells phagocytose and digest
bacterial proteins.
E. Peptides
from bacterial proteins appear on cell surfaces, bound to Class I MHC.
Questions 36-38: Déja vu all over again.
A
22-year-old college student with no significant previous illness comes to see
you after a trip to Mexico. On his third day in Cancun he developed watery
diarrhea which lasted two days. He had avoided salads and un-bottled water but
drank iced soft drinks from a stand on the beach. He did not see a physician or
take antibiotics. After returning he is well for about three weeks but again
develops diarrhea, this time bloody. He reports pain on passage of stool, which
is black and tarry. A stained smear of stool reveals many red and white cells,
amoeboid forms which contain ingested erythrocytes, and cyst forms. Endoscopy
reveals ulcerations of his colonic mucosa. He is started on an appropriate drug
but two days later develops fever and septicemia, likely produced by spread of
intestinal flora to the bloodstream from the ulcers in his colon. He is treated
with a combination of broad-spectrum antibiotics and makes a full recovery.
About a month later, he develops a second episode of bloody diarrhea. This
time, no amoeboid forms can be seen in stool smears. Gram stain of stool now
shows only ‘normal flora’.
Culture (on
appropriate media) for bacterial pathogens is also negative.
Answer each
question from the list of organisms below them.
36. _____
Which organism was most likely to have caused the patient’s original episode of
watery diarrhea?
37. _____
Which organism is most likely to have caused the patient’s bloody diarrhea,
three weeks after returning from Mexico?
38. _____
His course of broad-spectrum antibiotics should raise suspicion of what
organism, as the cause of his third episode of diarrhea?
A.
Balantidium coli
B.
Campylobacter jejuni
C. Clostridium difficile
D.
Cryptosporidium parvum
E. Entamobea histolytica
F. Escherichia coli
G. Giardia
lamblia
H.
Salmonella enterica
I. Shigella
dysenteriae
J. Vibrio
cholerae
Questions 39-40: A young woman with white lesions
on her oral mucosa.
39. _____ A
28-year old woman comes to clinic because creamy white patches have developed
on the lining of her oral cavity. A smear of a scraping from a lesion contains
budding yeast and pseudohyphae. Culture grows out creamy white colonies of
budding yeast. When yeast cells are suspended in plasma, buds elongate to form
the beginnings of hyphae.
Which
fungus is most likely in this setting?
A.
Histoplasma capsulatum
B.
Coccidiodes immitis.
C. Candida albicans
D.
Cryptococcus neoformans
E.
Paracoccidiodes braziliensis
F.
Sporothrix schenckii
G.
Pneumocystis carinii
40. _____
When the organism is examined under the microscope after culture on corn meal
agar, it appears as sketched at right.
Which
phrase best describes these forms?
A. Mixture
of mold and yeast forms
B. Hyphae,
arthroconidia, and microconidia
C. Hyphae,
rhizoids, and sporangia
D. Hyphae,
basidia, and chains of conidia
E. Hyphae, microconidia, and chlamydospores
Questions 41-43: A young boy with repeated
bacterial infections.
A
8-month-old boy has a middle ear infection. Exudate contains Gram-positive
cocci, many in pairs. Local lymph nodes and tonsils are barely visible; you
would have expected both to be swollen. His medical history includes numerous
similar infections caused by non-encapsulated Haemophilus influenzae,
Streptococcus pneumoniae, and Moraxella catarrhalis, a Gram-negative coccus;
pneumonia at 5 months, for which he was hospitalized; and a staphylococcal skin
infection, which responded poorly to antibiotics, at 6 months. Blood cultures
from the pneumonia grew Streptococcus pneumoniae. Family history reveals a male
cousin who died at age 14 months from pneumonia.
41. _____
If the cause of his present illness is S. pneumoniae, what initial report would
you expect from the lab?
A. G+ cocci, catalase-negative, α-hemolytic on
sheep blood agar
B. G+
cocci, catalase-negative β-hemolytic on sheep blood agar
C. G+
cocci, catalase-negative, γ-hemolytic on sheep blood agar
D. G+
cocci, catalase-positive, α-hemolytic on sheep blood agar
E. G+
cocci, catalase-positive, β-hemolytic on sheep blood agar
42. _____
If the patient has an immunodeficiency syndrome, what aspect of the immune
system is most likely to be defective?
A. IgM/IgG, complement, and neutrophils
B. IgE,
mast cells, and basophils
C. Fucntion
of CD4+ T cells
D.
Proliferation and cytolysis by CD8+ cells
E. Natural
killer cell function
43. _____
The patient remained healthy until he was five months old.
What is the
most likely reason that he did not develop infections before the age of five
months?
A. Babies
of that age range are not exposed to bacteria.
B. Maternal IgG provided protection.
C. During
the first few months of life the phagocytic capacity of neutrophils is high,
but then declines.
D.
Before5-6 months the intestine contains no ‘normal flora’.
E. Factors
H and I are not produced during the first six months of life, so that
Complement is more active then than later.
44. ____ A
20-year old college student with no previous history of significant illness
comes to clinic because of ten days of low fever, dry cough, and malaise. Chest
x-ray shows widespread diffuse inflammation of the lungs. She is given a
prescription of an erythromycin-class drug, because a common bacterial cause of
this type of illness in college students is resistant to all beta-lactam
antibiotics. Which organism below best fits this description?
A.
Staphylococcus aureus
B.
Streptococcus pneumoniae
C. Coxiella
burnetii
D. Mycoplasma pneumoniae
E. Chlamydia pneumonia
45. ____
Envelopes of Pseudomonas aeruginosa are much less permeable to antibiotics than
envelopes of Escherichia coli. Which of the following is most likely to account
for the difference?
A. Polar
vs. peritrichous flagella
B.
Thickness of peptidoglycan
C. Type of porin proteins in the outer
membrane
D. Presence
or absence of common pili
E. Type of
teichoic acid present
46. ____
Isolates of Streptococcus pneumoniae which cause invasive disease are
heavily-encapsulated. Isolates that lack capsules are much less virulent. How
do capsules facilitate development of invasive disease?
A. Toxic to
antibody-producing plasma cells.
B. Block
transport of protein antigens to lymph nodes.
C. Prevent phagocytosis by neutrophils.
D. Inhibit
cytokine production by Helper T cells.
E. Bind IgG
and prevents activation of complement.
47. ____ An
engineer recently returned from South America develops high fevers. Fever is
nearly continuous but there is some indication that it peaks every other day. A
blood smear prepared during a febrile interval is illustrated at right.
Which
organism is the most likely cause of this illness?
A. Plasmodium falciparum
B.
Plasmodium malariae
C.
Plasmodium ovale
D.
Plasmodium vixax
E. Babesia
microti
48. ____
Salmonella enterica serotype typhi, unlike most other serotypes of Salmonella,
can evade killing by macrophages. How does “S. typhi” evade killing?
A. Injects proteins into macrophage cytosol
with a Type III secretion system
B. Secretes
a protein exotoxin that kills macrophages
C. Once
phagocytosed, secretes a phospholipase that destroys the membrane of the
phagosome
D. Produces
an extracellular adenyl cyclase that inhibits phagocytosis
E. Binds
tightly to the outer face of the macrophage plasma membrane
49. ____ A
12-year-old boy develops a heart murmur. To help confirm or rule out Acute
Rheumatic Fever, you should order a serological test for antibodies to a
specific bacterial antigen.
In this
test, which antigen should be uses?
A. Protein
A of Staphylococcus aureus
B. M protein of Streptococcus pyogenes
C. α-toxin
of Clostridium perfringens
D.
Filamentous hemagglutinin (fha) of Bordetella pertussis
E.
K1-antigen of Escherichia coli
50. ____ A
tourist from France develops watery diarrhea produced by a local New Jersey
strain of
enterotoxigenic
E. coli (ETEC). How did the E. coli toxin produce diarrhea?
A. ADP-ribosylated a large G protein,
stimulated mammalian adenyl cyclase
B. Cleaved
ribosomal RNA, inhibited protein synthesis by 80S ribosomes
C.
Protease, cleaved surface protein of membrane vesicles in cytoplasm of
mammalian cells
D.
Initiated polymerization of actin filaments adjacent to intracellular bacteria
E. Entered
intestinal epithelial cells, synthesized cyclic GMP in cytosol
51. _____ A
23-year-old woman comes to your office because, for 3 days, she has experienced
burning with urination, increased frequency of urination, and a continual
feeling that she needs to urinate. She does not have vaginal discharge, fever,
or flank pain. Rapid ‘dipstick’ urine tests are consistent with uncomplicated
cystitis. Culture of urine on standard media produces a lactose-fermenting Gram
negative rod.
In
situations such as this, what is the most likely pathogen?
•
Enterobacter faecium
•
Escherichia coli
•
Klebsiella pneumoniae
•
Proteus vulgaris
•
Pseudomonas aeruginosa
•
Serratia marcescens
•
Salmonella enterica
•
Shigella boydii (or other Shigella)
52. _____ A
burn patient develops infection of the burn wound. Culture of exudate on
Brain-Heart Infusion agar produces numerous green-pigmented colonies of a
Gram-negative rod. The organism grows well aerobically on standard media but
shows no evidence of acid production on differential media such as MacConkey,
Hektoen Enteric, or Triple-Sugar-Iron agars.
What is the
most likely organism?
A.
Bacteroides fragilis
B.
Campylobacter fetus
C.
Francisella tularensis
D. Pseudomonas aeruginosa
E.
Escherichia coli
53. _____ A
female patient comes to you because of vaginal itching and discharge.
Microscopic examination of an unstained wet mount of discharge reveals squamous
epithelial cells and the motile forms illustrated at right.
What organism
is this?
A. A
Microsporidian
B.
Toxoplasma gondii
C.
Cryptosporidium parvum
D. Giardia
lamblia
E. Trichomonas vaginalis
54. _____ A
patient develops fevers after returning to New Jersey from a safari vacation in
East Africa. A blood smear, taken at the height of an episode of fever, is
illustrated at right.
Which
organism is most likely to be the cause of his fever?
A. Trypanosoma
brucei brucei
B. Trypanosoma brucei rhodesiense
C.
Trypanosoma brucei gambesiense
D.
Trypanosoma cruzi
E. A dermotropic Leishmania
F. A
Leishmania that produce visceral infections
55. _____
An HIV-positive patient develops chronic intractable diarrhea. Stool smear
contains small acid-fast cyst forms. Which organism is the most likely cause of
the patient’s diarrhea?
A.
Toxoplasma gondii
B.
Sarcocystis hominis
C. Cryptosporidium parvum
D. Isospora
belli
E.
Mycobacterium avium-intracellulare
F.
Actinomyces israelii
56. ____ A
34-year-old man has fever and an extensive rash that extends to his palms and
soles.
You order
tests to confirm or rule out secondary Syphilis. If this is indeed secondary
Syphilis, what results do you expect?
Test for anti-cardiolipin“non-treponemal”
Abs Test for antibodies specific
forTreponema pallidum
A. Positive
Negative
B. Positive
Positive
C. Negative
Negative
D. Negative
Positive
57. ____ A
young woman presents with cervicitis. A stained smear of material swabbed from
the inflamed area contains cells with prominent peri-nuclear inclusions. Some
inclusions are so large that they fill nearly the entire cytoplasm. What
organism is the most likely cause of the cervicitis in this patient?
A.
Chlamydia pneumoniae
B. Chlamydia trachomatis
C.
Chlamydia psittaci
D.
Mycoplasma pneumoniae
E.
Mycoplasma hominis
F.
Ureaplasma urealyticum
58. ____
You suspect that a patient with febrile illness and rash might have infection
with a Rickettsia.
In a
biopsy, in what cells would you would expect to find these organisms
multiplying?
A.
Pneumocytes (cells that line the alveoli of the lung)
B.
Hepatocytes (liver cells)
C. B
lymphocytes
D.
Intestinal epithelial cells
E. Neurons
F. Endothelial cells
59. ____ An
elderly man with chronic heart and lung disease develops Legionella pneumonia.
By what
route was the infection most likely to have been acquired?
A. Respiratory route, from an infected
person.
B. Inhalation of aerosolized water from a
source containing protozoa.
C. Using
snuff that contained spores.
D.
Inhalation of spores from moldy hay.
E. Exposure
to livestock or animal products.
F.
Aerosolized cat or dog saliva.
60. ____ In
coastal Massachusetts there have been several recent cases of Tularemia,
acquired when a person operating a riding lawn mower ran over a dead or dying
rabbit, and aerosolized micro-organisms from the animal. What property of
Francisella tularensis makes possible its transmission in this bizarre fashion?
A. Short
O-antigen chains on the outer membrane.
B.
Production of an exotoxin with an extremely low lethal dose.
C. A
lipid-rich cell envelope which makes bacteria resistant to dessication.
D. A very low infectious dose.
E. A
capsule that has the same antigenic structure as human cell-surface
oligosaccharides.
61. ____ A
group of people eat dinner together at a local restaurant and about 1/3 of them
become ill. Several, including two pregnant women, become septicemic and one of
the women suffers a spontaneous abortion. A small, motile, aerobic,
β-hemolytic, Gram-positive rod is recovered from blood and other cultures from
many of those who became ill. It does not form spores.
Which
organism listed below is most to be the pathogen?
A. Bacillus
anthracis
B. Bacillus
cereus
C.
Leptospira interrogans
D. Borrelia
recurrentis
E. Listeria monocytogenes
62. ____ A
diabetic 78-year-old man develops a necrotic ulcer on his right foot. Infection
spreads rapidly and there is gas in soft tissues. His foot is amputated at the
ankle. Gram stain of exudate from the amputation site contains large
Gram-positive rods. The bacteria grow well anaerobically, producing large
β-hemolytic colonies on sheep blood agar, but do not grow aerobically.
What
organism is most probable in this setting?
A. Bacillus
anthracis
B. Bacillus
cereus
C.
Corynebacterium diphtheriae
D. Nocardia
asteroides
E.
Clostridium tetani
F. Clostridium perfringens
63. ____ A
patient presents with a slowly-developing pneumonia. Several opacities are seen
in a lung x-ray. On his second hospital day he develops high fever and
hypotension. In a stained smear of leukocytes from the buffy coat of blood tiny
intracellular yeast forms are seen. They are illustrated at right below. [When
blood is centrifuged a thick layer of red erythrocytes collects at the bottom
of the tube. Above this is a thin off-white layer that contains the white cells
- the “buffy coat”. Above the buffy coat is the clear pale-yellow plasma.]
What
organism is this most likely to be?
A.
Coccidiodes immitis
B.
Blastomyces dermatitidis
C. Histoplasma capsulatum
D.
Cryptococcus neoformans
E.
Pneumocystis carinii
F. Candida
albicans
64. _____ A
patient with a Gram-negative infection is treated with a cephalosporin, a
β-lactam antibiotic.
In
bacteria, what essential process is inhibited by β-lactams?
A.
Synthesis of disaccharide precursors of peptidoglycan.
B.
Transport of disaccharide precursors through the plasma membrane.
C.
Polymerization of peptidoglycan disaccharides into long chains.
D.
Conversion of L-alanine to D-alanine.
E.
Polymerization of the peptide side chains of peptidoglycan.
F. Cross-linking of the peptide side chains of
peptidoglycan.
65. ____
For an isolate of E. coli obtained from a blood culture, the lab reports
antibiotic Minimal Inhibitory Concentrations (MIC) as follows:
Drug MIC (μg/ml)
Ampicillin
(penicilin) 3
Ceftazidime
(cephalosporin)
0.03
Tetracycline
128
Which
conclusion best follows from these data?
A. On this
isolate, ampicillin will have only a bacteriostatic effect.
B. The
isolate is resistant to cephalosporins because it produces a TEM-type
β-lactamase
C. Of these
three drugs, tetracycline will be the most effective against this isolate.
D. Of these three drugs, ceftazidime will kill
this isolate at the lowest concentration.
E. When
used in combination, ampicillin and tetracycline will have synergistic effects.
Q: 71-77
Match each of the following agents with the corresponding features (choices may be used once, more than once or not at all):
A. Herpes simplex 1
B. Herpes simplex 2
C. Varicella-zoster virus
D. Cytomegalovirus
E. Epstein-Barr virus (EBV)
F. Human Herpesvirus 8 (HHV8)
71. _____ A child born deaf.(D)
72. _____ An AIDS patient presents with Kaposi’s Sarcoma (F)
73. _____ A 72-year-old male presents with a red blistery rash along the distribution of the 8th and 9th thoracic spinal nerve.(C)
74. _____ A sexually active 24-year-old patient presents with a blistery rash on the genitals.(B)
75. _____ A patient presents with severe encephalitis.(A & B)
76. _____ A 6-year-old child presents with severe rash and blistering on the cheeks, lips and in the mouth.(A)
77. _____ An adolescent patient presents with fatigue, fever, sore throat, enlargement of lymph nodes and an enlarged spleen.(E)
Q: 78-80
Match each of the following agents with the corresponding features (choices may be used once, more than once or not at all):
A. Clostridium tetani (A)
B. Clostridium botulinum (B)
C. Clostridium perfringens (C)
78. _____ Spastic paralysis
79. _____ Flaccid paralysis
80. _____ Gas-gangrene
