Stanford University MD INDE 247B Foundations of
Medicine V B – Microbiology Capstone,
Pharmacology Capstone, MIC/CMS Study Guide,
Original Practice Questions & Answers, Medical
School Exam Preparation, Comprehensive Medicine
Review, Clinical Microbiology, Infectious Diseases,
Antimicrobial Therapy, Pharmacology, Drug
Mechanisms, Adverse Effects, Drug Interactions,
Diagnostic Testing, Pathophysiology & Clinical
Applications
Question 1: A 45-year-old male presents with fever, chills, and a productive
cough with rusty sputum. A chest X-ray reveals right lower lobe consolidation.
Which of the following virulence factors is most directly responsible for the
alveolar damage and inflammatory response seen in this patient's most likely
condition?
A. Protein M
B. Lipoteichoic acid
C. Pneumolysin
D. Capsular polysaccharide
CORRECT ANSWER: C. Pneumolysin
Rationale: The patient's presentation is classic for community-acquired pneumonia
caused by Streptococcus pneumoniae. Pneumolysin is a pore-forming toxin that activates
the classical complement pathway, triggers a vigorous inflammatory response, and
causes direct damage to alveolar epithelial cells and endothelial cells, contributing to the
characteristic consolidation. While the capsule is the primary virulence factor for
evading phagocytosis, pneumolysin is most directly responsible for the tissue damage
and inflammation.
Question 2: A 28-year-old woman who recently traveled to the southwestern
United States develops fever, erythema nodosum, and a chest X-ray showing
bilateral hilar lymphadenopathy. A sputum fungal culture reveals a mold that
is highly infectious in the laboratory. Which of the following is the most
appropriate initial treatment for her condition?
A. Fluconazole
B. Itraconazole
C. Amphotericin B
D. Caspofungin
CORRECT ANSWER: B. Itraconazole
,Rationale: The clinical picture is consistent with acute primary coccidioidomycosis
(Valley fever), caused by Coccidioides immitis or posadasii. For patients with symptomatic
but uncomplicated primary pulmonary infection who require treatment, itraconazole or
fluconazole is recommended. Itraconazole is often favored for mild to moderate disease
due to its efficacy. Amphotericin B is reserved for severe or disseminated disease, and
caspofungin is not a primary agent for this fungus. The organism is a highly infectious
mold (arthroconidia) in the lab.
Question 3: A 55-year-old patient with diabetes mellitus and end-stage renal
disease on hemodialysis develops a fever and a painful, fluctuant swelling on
his forearm at the site of a previous arteriovenous fistula. Blood cultures are
positive for a gram-negative, oxidase-positive, non-lactose-fermenting rod.
Which of the following mechanisms of antimicrobial resistance is most likely
to be intrinsically present in this organism?
A. Modification of the drug target (PBP2a)
B. Efflux pumps for macrolides
C. Production of extended-spectrum beta-lactamases (ESBLs)
D. Chromosomal beta-lactamase (AmpC)
CORRECT ANSWER: D. Chromosomal beta-lactamase (AmpC)
Rationale: The patient's presentation and culture results are suspicious
for Stenotrophomonas maltophilia or Pseudomonas aeruginosa, but the oxidase-positive,
non-lactose-fermenting gram-negative rod in a hemodialysis patient with a device-
related infection is classic for Pseudomonas aeruginosa. P. aeruginosa has an intrinsic,
inducible chromosomal AmpC beta-lactamase that confers resistance to many
penicillins and cephalosporins. This is an inherent property of the organism, not an
acquired one like ESBL or PBP2a.
Question 4: A 32-year-old immunocompromised patient develops a vesicular
rash that is unilateral and follows a dermatomal distribution on his trunk. He
reports a history of chickenpox as a child. Which of the following best
describes the mechanism by which the causative virus establishes latency and
reactivates?
A. The virus integrates its DNA into the host cell chromosome.
B. The virus establishes latency in sensory ganglia as a non-replicating episome.
C. The virus remains in a latent state in circulating B-lymphocytes.
D. The virus maintains latency in epithelial cells of the skin.
CORRECT ANSWER: B. The virus establishes latency in sensory ganglia as a
non-replicating episome.
,Rationale: The patient has herpes zoster (shingles) caused by reactivation of the
varicella-zoster virus (VZV). After primary infection (chickenpox), VZV travels
retrograde along sensory nerves to establish latency in the nuclei of sensory ganglia
(e.g., dorsal root ganglia) where it persists as a circular episome without integrating into
the host genome. Reactivation occurs when cell-mediated immunity wanes, leading to
viral replication and anterograde transport back to the skin.
Question 5: A 60-year-old man with chronic obstructive pulmonary disease
(COPD) is hospitalized with an exacerbation. A sputum culture shows a gram-
negative coccobacillus that is oxidase-negative, urease-positive, and produces
a yellow pigment on agar. This organism is a common cause of lower
respiratory tract infections in patients with structural lung disease. Which of
the following is a key virulence factor that allows this organism to adhere to
respiratory epithelial cells?
A. Pertussis toxin
B. Tracheal cytotoxin
C. Pili (fimbriae)
D. Lipooligosaccharide (LOS)
CORRECT ANSWER: C. Pili (fimbriae)
Rationale: The organism described is Burkholderia cepacia complex or Bordetella
bronchiseptica, but the description of a yellow-pigmented, oxidase-negative, urease-
positive coccobacillus in COPD patients is classic for Burkholderia cepacia. While B.
cepacia expresses multiple virulence factors, its pili (fimbriae) are crucial for adherence
to respiratory epithelial cells and mucus, a critical first step in colonization and infection.
Tracheal cytotoxin is a virulence factor for Bordetella pertussis.
Question 6: A 7-year-old child presents with a sore throat, fever, and exudative
tonsillitis. A rapid antigen detection test for Group A Streptococcus is positive.
The child has a history of a severe allergy to penicillin. Which of the following
is the most appropriate alternative antibiotic for treating this infection?
A. Erythromycin
B. Doxycycline
C. Clindamycin
D. Azithromycin
CORRECT ANSWER: C. Clindamycin
Rationale: For a patient with a severe penicillin allergy (e.g., anaphylaxis) and confirmed
Group A Streptococcus (GAS) pharyngitis, clindamycin is a recommended alternative.
While macrolides like erythromycin and azithromycin are alternatives, resistance to
macrolides is increasingly common in GAS. Clindamycin is also effective and has a
, different mechanism of action. Doxycycline is not recommended for children under 8
years of age due to dental staining and is less effective for GAS.
Question 7: A patient with a history of recurrent pyelonephritis is being
treated for a urinary tract infection caused by Escherichia coli. The organism is
found to be resistant to ampicillin and first-generation cephalosporins. Further
testing reveals the presence of a plasmid-encoded enzyme that hydrolyzes
penicillin and cephalosporins but is inhibited by clavulanate. Which of the
following best describes this resistance mechanism?
A. TEM-1 beta-lactamase
B. AmpC beta-lactamase
C. Metallo-beta-lactamase (MBL)
D. KPC carbapenemase
CORRECT ANSWER: A. TEM-1 beta-lactamase
Rationale: TEM-1 is one of the most common plasmid-encoded beta-lactamases found
in gram-negative bacteria like E. coli. It hydrolyzes penicillins and early cephalosporins.
Its activity is inhibited by beta-lactamase inhibitors like clavulanate, sulbactam, and
tazobactam. AmpC is a chromosomal cephalosporinase not typically inhibited by
clavulanate. MBLs and KPC are carbapenemases, which have broader activity and are
not typically inhibited by clavulanate.
Question 8: A 25-year-old veterinary student develops a febrile illness with
headache, myalgia, and conjunctival suffusion after assisting in a bovine
delivery. She reports that the calf was stillborn. Which of the following is the
most likely causative agent, and what is the primary mode of transmission?
A. Brucella abortus, inhalation of aerosols
B. Leptospira interrogans, contact with urine-contaminated water
C. Coxiella burnetii, inhalation of aerosols
D. Francisella tularensis, tick bite
CORRECT ANSWER: C. Coxiella burnetii, inhalation of aerosols
Rationale: The scenario describes Q fever, caused by Coxiella burnetii. The organism is
highly infectious and is transmitted to humans primarily through the inhalation of
aerosols from placental tissue, amniotic fluid, or urine of infected animals, particularly
during parturition. Veterinary students and farmers are at high risk. While Brucella can
also cause a febrile illness and is associated with animal contact, the specific association
with a stillborn calf and aerosol transmission is most characteristic of C. burnetii.
Medicine V B – Microbiology Capstone,
Pharmacology Capstone, MIC/CMS Study Guide,
Original Practice Questions & Answers, Medical
School Exam Preparation, Comprehensive Medicine
Review, Clinical Microbiology, Infectious Diseases,
Antimicrobial Therapy, Pharmacology, Drug
Mechanisms, Adverse Effects, Drug Interactions,
Diagnostic Testing, Pathophysiology & Clinical
Applications
Question 1: A 45-year-old male presents with fever, chills, and a productive
cough with rusty sputum. A chest X-ray reveals right lower lobe consolidation.
Which of the following virulence factors is most directly responsible for the
alveolar damage and inflammatory response seen in this patient's most likely
condition?
A. Protein M
B. Lipoteichoic acid
C. Pneumolysin
D. Capsular polysaccharide
CORRECT ANSWER: C. Pneumolysin
Rationale: The patient's presentation is classic for community-acquired pneumonia
caused by Streptococcus pneumoniae. Pneumolysin is a pore-forming toxin that activates
the classical complement pathway, triggers a vigorous inflammatory response, and
causes direct damage to alveolar epithelial cells and endothelial cells, contributing to the
characteristic consolidation. While the capsule is the primary virulence factor for
evading phagocytosis, pneumolysin is most directly responsible for the tissue damage
and inflammation.
Question 2: A 28-year-old woman who recently traveled to the southwestern
United States develops fever, erythema nodosum, and a chest X-ray showing
bilateral hilar lymphadenopathy. A sputum fungal culture reveals a mold that
is highly infectious in the laboratory. Which of the following is the most
appropriate initial treatment for her condition?
A. Fluconazole
B. Itraconazole
C. Amphotericin B
D. Caspofungin
CORRECT ANSWER: B. Itraconazole
,Rationale: The clinical picture is consistent with acute primary coccidioidomycosis
(Valley fever), caused by Coccidioides immitis or posadasii. For patients with symptomatic
but uncomplicated primary pulmonary infection who require treatment, itraconazole or
fluconazole is recommended. Itraconazole is often favored for mild to moderate disease
due to its efficacy. Amphotericin B is reserved for severe or disseminated disease, and
caspofungin is not a primary agent for this fungus. The organism is a highly infectious
mold (arthroconidia) in the lab.
Question 3: A 55-year-old patient with diabetes mellitus and end-stage renal
disease on hemodialysis develops a fever and a painful, fluctuant swelling on
his forearm at the site of a previous arteriovenous fistula. Blood cultures are
positive for a gram-negative, oxidase-positive, non-lactose-fermenting rod.
Which of the following mechanisms of antimicrobial resistance is most likely
to be intrinsically present in this organism?
A. Modification of the drug target (PBP2a)
B. Efflux pumps for macrolides
C. Production of extended-spectrum beta-lactamases (ESBLs)
D. Chromosomal beta-lactamase (AmpC)
CORRECT ANSWER: D. Chromosomal beta-lactamase (AmpC)
Rationale: The patient's presentation and culture results are suspicious
for Stenotrophomonas maltophilia or Pseudomonas aeruginosa, but the oxidase-positive,
non-lactose-fermenting gram-negative rod in a hemodialysis patient with a device-
related infection is classic for Pseudomonas aeruginosa. P. aeruginosa has an intrinsic,
inducible chromosomal AmpC beta-lactamase that confers resistance to many
penicillins and cephalosporins. This is an inherent property of the organism, not an
acquired one like ESBL or PBP2a.
Question 4: A 32-year-old immunocompromised patient develops a vesicular
rash that is unilateral and follows a dermatomal distribution on his trunk. He
reports a history of chickenpox as a child. Which of the following best
describes the mechanism by which the causative virus establishes latency and
reactivates?
A. The virus integrates its DNA into the host cell chromosome.
B. The virus establishes latency in sensory ganglia as a non-replicating episome.
C. The virus remains in a latent state in circulating B-lymphocytes.
D. The virus maintains latency in epithelial cells of the skin.
CORRECT ANSWER: B. The virus establishes latency in sensory ganglia as a
non-replicating episome.
,Rationale: The patient has herpes zoster (shingles) caused by reactivation of the
varicella-zoster virus (VZV). After primary infection (chickenpox), VZV travels
retrograde along sensory nerves to establish latency in the nuclei of sensory ganglia
(e.g., dorsal root ganglia) where it persists as a circular episome without integrating into
the host genome. Reactivation occurs when cell-mediated immunity wanes, leading to
viral replication and anterograde transport back to the skin.
Question 5: A 60-year-old man with chronic obstructive pulmonary disease
(COPD) is hospitalized with an exacerbation. A sputum culture shows a gram-
negative coccobacillus that is oxidase-negative, urease-positive, and produces
a yellow pigment on agar. This organism is a common cause of lower
respiratory tract infections in patients with structural lung disease. Which of
the following is a key virulence factor that allows this organism to adhere to
respiratory epithelial cells?
A. Pertussis toxin
B. Tracheal cytotoxin
C. Pili (fimbriae)
D. Lipooligosaccharide (LOS)
CORRECT ANSWER: C. Pili (fimbriae)
Rationale: The organism described is Burkholderia cepacia complex or Bordetella
bronchiseptica, but the description of a yellow-pigmented, oxidase-negative, urease-
positive coccobacillus in COPD patients is classic for Burkholderia cepacia. While B.
cepacia expresses multiple virulence factors, its pili (fimbriae) are crucial for adherence
to respiratory epithelial cells and mucus, a critical first step in colonization and infection.
Tracheal cytotoxin is a virulence factor for Bordetella pertussis.
Question 6: A 7-year-old child presents with a sore throat, fever, and exudative
tonsillitis. A rapid antigen detection test for Group A Streptococcus is positive.
The child has a history of a severe allergy to penicillin. Which of the following
is the most appropriate alternative antibiotic for treating this infection?
A. Erythromycin
B. Doxycycline
C. Clindamycin
D. Azithromycin
CORRECT ANSWER: C. Clindamycin
Rationale: For a patient with a severe penicillin allergy (e.g., anaphylaxis) and confirmed
Group A Streptococcus (GAS) pharyngitis, clindamycin is a recommended alternative.
While macrolides like erythromycin and azithromycin are alternatives, resistance to
macrolides is increasingly common in GAS. Clindamycin is also effective and has a
, different mechanism of action. Doxycycline is not recommended for children under 8
years of age due to dental staining and is less effective for GAS.
Question 7: A patient with a history of recurrent pyelonephritis is being
treated for a urinary tract infection caused by Escherichia coli. The organism is
found to be resistant to ampicillin and first-generation cephalosporins. Further
testing reveals the presence of a plasmid-encoded enzyme that hydrolyzes
penicillin and cephalosporins but is inhibited by clavulanate. Which of the
following best describes this resistance mechanism?
A. TEM-1 beta-lactamase
B. AmpC beta-lactamase
C. Metallo-beta-lactamase (MBL)
D. KPC carbapenemase
CORRECT ANSWER: A. TEM-1 beta-lactamase
Rationale: TEM-1 is one of the most common plasmid-encoded beta-lactamases found
in gram-negative bacteria like E. coli. It hydrolyzes penicillins and early cephalosporins.
Its activity is inhibited by beta-lactamase inhibitors like clavulanate, sulbactam, and
tazobactam. AmpC is a chromosomal cephalosporinase not typically inhibited by
clavulanate. MBLs and KPC are carbapenemases, which have broader activity and are
not typically inhibited by clavulanate.
Question 8: A 25-year-old veterinary student develops a febrile illness with
headache, myalgia, and conjunctival suffusion after assisting in a bovine
delivery. She reports that the calf was stillborn. Which of the following is the
most likely causative agent, and what is the primary mode of transmission?
A. Brucella abortus, inhalation of aerosols
B. Leptospira interrogans, contact with urine-contaminated water
C. Coxiella burnetii, inhalation of aerosols
D. Francisella tularensis, tick bite
CORRECT ANSWER: C. Coxiella burnetii, inhalation of aerosols
Rationale: The scenario describes Q fever, caused by Coxiella burnetii. The organism is
highly infectious and is transmitted to humans primarily through the inhalation of
aerosols from placental tissue, amniotic fluid, or urine of infected animals, particularly
during parturition. Veterinary students and farmers are at high risk. While Brucella can
also cause a febrile illness and is associated with animal contact, the specific association
with a stillborn calf and aerosol transmission is most characteristic of C. burnetii.
