Sherris Microbiology
A man presents to urgent care with a history of fever, a shaking chill, and the production of
reddish-colored sputum. The X-ray shows consolidation of the right middle lobe of the lung, and
a Gram stain of the sputum shows numerous neutrophils and lancet-shaped gram-positive
diplococci. External to the cell wall of this organism is typically found:
A
Flagella
B
Pili
C
Lipopolysaccharide
D
Polysaccharide
E
Exotoxin - ANS Explanation:
ANSWER: D - This is pneumococcal pneumonia involving a polysaccharide capsule.
Answer analysis:
A. Not a virulence factor for S. pneumoniae.
B. Same as above.
C. Only present in gram-negatives.
D. CORRECT - The pneumococcus is avirulant without its capsule.
E. Pneumolysin may contribute to lung symptoms.
A 70-year-old woman has collapsed following weeks of nausea and upper abdominal paid. In
the emergency room she is discovered to have a perforated gastric ulcer. Which of the following
features is significant in both the pathogenesis and diagnosis of this disease?
A
Coagulase
B
Urease
C
CagA protein
D
Superantigen exotoxin
E
Alginate - ANS ANSWER: B - This is Helicobacter pylori disease. The potent urease assists H.
pylori survival in the acid stomach.
Answer analysis:
A. Staphylococcus aureus diagnosis.
B. CORRECT - Urease activity in gastric secretions can be detected in less than an hour.
,C. Important in pathogenesis but not diagnosis
D. Staph or strep toxic shock syndrome.
E. Pseudomonas biofilm
In the investigation of a young man's vague inflammatory complains cells with large cytoplasmic
inclusions were discovered in the cerebrospinal fluid. He recalled tick bites after a recent hike in
Georgia. Molecular methods later identified Ehrlichia chaffeensis as the etiologic agent. The
cytoplasmic inclusions seen were most likely in:
A
Meningeal epithelial cells
B
Schwan cells
C
Polymorphonuclear leukocytes
D
Granulocytes
E
Mononuclear leukocytes - ANS ANSWER: E - The disease is called human monocytic
ehrlichiosis.
Answer analysis:
A. Not involved
B. Not involved
C. May be present by not with inclusions
D. The target for a similar disease, human granulocytic anaplasmosis
E. CORRECT - Transmitted by ticks from a deer reservoir
Twelve hours after birth a newborn is lethargic and feeding poorly. A blood culture reveals
gram-positive cocci in short chains which are catalase negative. The cell wall of this organism
most certainly contains:
A
Pili
B
Flagella
C
Lipopolysaccharide
D
Outer membrane
E
Peptidoglycan - ANS ANSWER: E - This is neonatal group B streptococcal sepsis.
Answer analysis:
A. Not a virulence factor for GBS.
B. Same as above
C. Only in gram negatives
D. Same as above.
,E. Peptidoglycan is prominent is all gram-positive bacteria.
As part of an annual evaluation, a 30-year-old medical resident's tuberculin skin test shows 16
mm induration. She has always had negative tests in the past including one a year earlier. She
is afebrile, feels well, and her chest X-ray is clear. The best course of action at this point is:
A
Sputum acid-fast stain
B
Sputum TB culture
C
Bronchoalveolar lavage (BAL) with culture
D
3 drug TB therapy
E
Isoniazid chemoprophylaxis - ANS ANSWER: E - This will reduce the chances of evolution to
active tuberculosis.
Answer analysis:
A. Useful only if clinical or radiologic signs of disease are present.
B. Same as above
C. Same as above
D. Too aggressive with no signs of disease
E. CORRECT - Prevention is most successful with a recent skin test converter.
A transient man is seen in the emergency room for fever, chills, and a productive cough. The
episode began suddenly with a severe shaking chill. A Gram stain of his sputum shows
gram-positive cocci in pairs and his chest X-ray shows consolidation of the right middle lobe.
Which feature of the bacterium was most important in the initiation of this infection?
A
Pili adhering to tracheal mucosa
B
Polysaccharide interference with complement
C
Catalase generating superoxide ions
D
Superantigen generation of cytokines
E
Cell injury by pore-forming toxi - ANS ANSWER: B - Its capsule interferes with C3b deposition
on the pneumococcal surface.
Answer analysis:
A. Pili not involved.
B. CORRECT - The result is blocking ingestion by professional phagocytes.
C. Pneumococci do not produce catalase.
D. No superantigens produced
E. No pore-forming toxins produced.
, A woman has been in the hospital for 3 weeks due to complications following surgery for colon
cancer. Five days into a course of ceftriaxone for suspected pneumonia she developed
diarrhea. Colonoscopy revealed multiple plaques on the mucosa which are composed of fibrin
and WBS. Stool examinations for Salmonella, Shigella, Campylobacter, and amoebas are
negative. The diarrhea and plaques are most likely produced by:
A
Endotoxin from clostridial spores
B
Exotoxin from clostridial spores
C
Exotoxin from clostridial cells
D
Labile Toxin from E coli cells
E
Endotoxin from E coli cells - ANS ANSWER: C -Clostridium difficile produces potent exotoxins
when able to multiply freely in the intestine.
Answer analysis:
A. Neither clostridial cells or spores contain endotoxin
B. Spores are inert producing no metabolic products
C. CORRECT - The ceftriaxone gave C. difficile an "edge" by inhibiting competing flora.
D. LT causes a watery diarrhea with no enteric cell injury.
E. Endotoxin does not cause diarrhea.
Multiple newborns have developed diarrhea while still in the nursery. Routine stool cultures were
negative, but a molecular panel detected an E. coli strain associated with intestinal disease. If
the stool shows no blood but the mucosa show pedestal-like extensions this strain most likely
produces:
A
Shiga toxin (Stx)
B
Labile toxin (LT)
C
Attaching and effacing (A/E) lesions
D
Invasion, ulcers
E
A and B
F
A and C - ANS ANSWER: C - This is enteropathogenic E. coli produced by the A/E lesions and
other proteins secreted into the enterocyte cytoplasm.
Answer analysis:
A. Combined with A/E lesions in enterohemorrhagic syndrome.
B. Enterotoxigenic E. coli.
A man presents to urgent care with a history of fever, a shaking chill, and the production of
reddish-colored sputum. The X-ray shows consolidation of the right middle lobe of the lung, and
a Gram stain of the sputum shows numerous neutrophils and lancet-shaped gram-positive
diplococci. External to the cell wall of this organism is typically found:
A
Flagella
B
Pili
C
Lipopolysaccharide
D
Polysaccharide
E
Exotoxin - ANS Explanation:
ANSWER: D - This is pneumococcal pneumonia involving a polysaccharide capsule.
Answer analysis:
A. Not a virulence factor for S. pneumoniae.
B. Same as above.
C. Only present in gram-negatives.
D. CORRECT - The pneumococcus is avirulant without its capsule.
E. Pneumolysin may contribute to lung symptoms.
A 70-year-old woman has collapsed following weeks of nausea and upper abdominal paid. In
the emergency room she is discovered to have a perforated gastric ulcer. Which of the following
features is significant in both the pathogenesis and diagnosis of this disease?
A
Coagulase
B
Urease
C
CagA protein
D
Superantigen exotoxin
E
Alginate - ANS ANSWER: B - This is Helicobacter pylori disease. The potent urease assists H.
pylori survival in the acid stomach.
Answer analysis:
A. Staphylococcus aureus diagnosis.
B. CORRECT - Urease activity in gastric secretions can be detected in less than an hour.
,C. Important in pathogenesis but not diagnosis
D. Staph or strep toxic shock syndrome.
E. Pseudomonas biofilm
In the investigation of a young man's vague inflammatory complains cells with large cytoplasmic
inclusions were discovered in the cerebrospinal fluid. He recalled tick bites after a recent hike in
Georgia. Molecular methods later identified Ehrlichia chaffeensis as the etiologic agent. The
cytoplasmic inclusions seen were most likely in:
A
Meningeal epithelial cells
B
Schwan cells
C
Polymorphonuclear leukocytes
D
Granulocytes
E
Mononuclear leukocytes - ANS ANSWER: E - The disease is called human monocytic
ehrlichiosis.
Answer analysis:
A. Not involved
B. Not involved
C. May be present by not with inclusions
D. The target for a similar disease, human granulocytic anaplasmosis
E. CORRECT - Transmitted by ticks from a deer reservoir
Twelve hours after birth a newborn is lethargic and feeding poorly. A blood culture reveals
gram-positive cocci in short chains which are catalase negative. The cell wall of this organism
most certainly contains:
A
Pili
B
Flagella
C
Lipopolysaccharide
D
Outer membrane
E
Peptidoglycan - ANS ANSWER: E - This is neonatal group B streptococcal sepsis.
Answer analysis:
A. Not a virulence factor for GBS.
B. Same as above
C. Only in gram negatives
D. Same as above.
,E. Peptidoglycan is prominent is all gram-positive bacteria.
As part of an annual evaluation, a 30-year-old medical resident's tuberculin skin test shows 16
mm induration. She has always had negative tests in the past including one a year earlier. She
is afebrile, feels well, and her chest X-ray is clear. The best course of action at this point is:
A
Sputum acid-fast stain
B
Sputum TB culture
C
Bronchoalveolar lavage (BAL) with culture
D
3 drug TB therapy
E
Isoniazid chemoprophylaxis - ANS ANSWER: E - This will reduce the chances of evolution to
active tuberculosis.
Answer analysis:
A. Useful only if clinical or radiologic signs of disease are present.
B. Same as above
C. Same as above
D. Too aggressive with no signs of disease
E. CORRECT - Prevention is most successful with a recent skin test converter.
A transient man is seen in the emergency room for fever, chills, and a productive cough. The
episode began suddenly with a severe shaking chill. A Gram stain of his sputum shows
gram-positive cocci in pairs and his chest X-ray shows consolidation of the right middle lobe.
Which feature of the bacterium was most important in the initiation of this infection?
A
Pili adhering to tracheal mucosa
B
Polysaccharide interference with complement
C
Catalase generating superoxide ions
D
Superantigen generation of cytokines
E
Cell injury by pore-forming toxi - ANS ANSWER: B - Its capsule interferes with C3b deposition
on the pneumococcal surface.
Answer analysis:
A. Pili not involved.
B. CORRECT - The result is blocking ingestion by professional phagocytes.
C. Pneumococci do not produce catalase.
D. No superantigens produced
E. No pore-forming toxins produced.
, A woman has been in the hospital for 3 weeks due to complications following surgery for colon
cancer. Five days into a course of ceftriaxone for suspected pneumonia she developed
diarrhea. Colonoscopy revealed multiple plaques on the mucosa which are composed of fibrin
and WBS. Stool examinations for Salmonella, Shigella, Campylobacter, and amoebas are
negative. The diarrhea and plaques are most likely produced by:
A
Endotoxin from clostridial spores
B
Exotoxin from clostridial spores
C
Exotoxin from clostridial cells
D
Labile Toxin from E coli cells
E
Endotoxin from E coli cells - ANS ANSWER: C -Clostridium difficile produces potent exotoxins
when able to multiply freely in the intestine.
Answer analysis:
A. Neither clostridial cells or spores contain endotoxin
B. Spores are inert producing no metabolic products
C. CORRECT - The ceftriaxone gave C. difficile an "edge" by inhibiting competing flora.
D. LT causes a watery diarrhea with no enteric cell injury.
E. Endotoxin does not cause diarrhea.
Multiple newborns have developed diarrhea while still in the nursery. Routine stool cultures were
negative, but a molecular panel detected an E. coli strain associated with intestinal disease. If
the stool shows no blood but the mucosa show pedestal-like extensions this strain most likely
produces:
A
Shiga toxin (Stx)
B
Labile toxin (LT)
C
Attaching and effacing (A/E) lesions
D
Invasion, ulcers
E
A and B
F
A and C - ANS ANSWER: C - This is enteropathogenic E. coli produced by the A/E lesions and
other proteins secreted into the enterocyte cytoplasm.
Answer analysis:
A. Combined with A/E lesions in enterohemorrhagic syndrome.
B. Enterotoxigenic E. coli.
