BIOL 271 MICROBIOLOGY WITH LAB
CASE STUDY QUIZZES 2
1. A 22-year-old college student presents with high fever, headache, and a petechial rash.
Lumbar puncture reveals cloudy CSF with increased neutrophils, high protein, and low
glucose. Gram stain shows Gram-negative diplococci. Which of the following is the most likely
causative agent?
A. Streptococcus pneumoniae
B. Listeria monocytogenes
C. Haemophilus influenzae
D. Neisseria meningitidis
Answer: D
Conceptual Explanation: Neisseria meningitidis is a Gram-negative diplococcus that
commonly causes meningitis in young adults, often presenting with a characteristic
petechial rash. CSF findings of low glucose and high protein are consistent with bacterial
meningitis.
,2. A 65-year-old male with chronic obstructive pulmonary disease (COPD) presents with a
productive cough and fever. Gram stain of the sputum shows Gram-positive Lancet-shaped
diplococci. What is the most likely organism?
A. Mycoplasma pneumoniae
B. Staphylococcus aureus
C. Klebsiella pneumoniae
D. Streptococcus pneumoniae
Answer: D
Conceptual Explanation: Streptococcus pneumoniae is classically described as Gram-
positive, lancet-shaped diplococci. It is the most common cause of community-acquired
pneumonia.
3. A 30-year-old patient who recently completed a course of clindamycin for a skin infection
presents with profuse, foul-smelling diarrhea and abdominal cramping. A toxin assay for
which organism should be performed?
A. Salmonella enterica
B. Shigella sonnei
C. Clostridioides difficile
D. Campylobacter jejuni
Answer: C
, Conceptual Explanation: Antibiotic use, particularly clindamycin, is a major risk factor for
Clostridioides difficile infection due to the disruption of normal gut flora, allowing C. diff to
overgrow and release toxins.
4. A 45-year-old patient with poorly controlled diabetes presents with a black, necrotic lesion
on the nasal turbinates (mucormycosis). A biopsy shows non-septate hyphae branching at 90-
degree angles. Which genus is likely involved?
A. Rhizopus
B. Aspergillus
C. Candida
D. Cryptococcus
Answer: A
Conceptual Explanation: Rhizopus and Mucor species are known for causing
rhinocerebral mucormycosis in diabetic patients, characterized by broad, non-septate
hyphae with right-angle branching.
5. A patient presents with a painless ulcer (chancre) on the genitalia. Dark-field microscopy of
the lesion exudate reveals spiral-shaped organisms. What is the diagnosis?
A. Chlamydia trachomatis
B. Neisseria gonorrhoeae
C. Haemophilus ducreyi
CASE STUDY QUIZZES 2
1. A 22-year-old college student presents with high fever, headache, and a petechial rash.
Lumbar puncture reveals cloudy CSF with increased neutrophils, high protein, and low
glucose. Gram stain shows Gram-negative diplococci. Which of the following is the most likely
causative agent?
A. Streptococcus pneumoniae
B. Listeria monocytogenes
C. Haemophilus influenzae
D. Neisseria meningitidis
Answer: D
Conceptual Explanation: Neisseria meningitidis is a Gram-negative diplococcus that
commonly causes meningitis in young adults, often presenting with a characteristic
petechial rash. CSF findings of low glucose and high protein are consistent with bacterial
meningitis.
,2. A 65-year-old male with chronic obstructive pulmonary disease (COPD) presents with a
productive cough and fever. Gram stain of the sputum shows Gram-positive Lancet-shaped
diplococci. What is the most likely organism?
A. Mycoplasma pneumoniae
B. Staphylococcus aureus
C. Klebsiella pneumoniae
D. Streptococcus pneumoniae
Answer: D
Conceptual Explanation: Streptococcus pneumoniae is classically described as Gram-
positive, lancet-shaped diplococci. It is the most common cause of community-acquired
pneumonia.
3. A 30-year-old patient who recently completed a course of clindamycin for a skin infection
presents with profuse, foul-smelling diarrhea and abdominal cramping. A toxin assay for
which organism should be performed?
A. Salmonella enterica
B. Shigella sonnei
C. Clostridioides difficile
D. Campylobacter jejuni
Answer: C
, Conceptual Explanation: Antibiotic use, particularly clindamycin, is a major risk factor for
Clostridioides difficile infection due to the disruption of normal gut flora, allowing C. diff to
overgrow and release toxins.
4. A 45-year-old patient with poorly controlled diabetes presents with a black, necrotic lesion
on the nasal turbinates (mucormycosis). A biopsy shows non-septate hyphae branching at 90-
degree angles. Which genus is likely involved?
A. Rhizopus
B. Aspergillus
C. Candida
D. Cryptococcus
Answer: A
Conceptual Explanation: Rhizopus and Mucor species are known for causing
rhinocerebral mucormycosis in diabetic patients, characterized by broad, non-septate
hyphae with right-angle branching.
5. A patient presents with a painless ulcer (chancre) on the genitalia. Dark-field microscopy of
the lesion exudate reveals spiral-shaped organisms. What is the diagnosis?
A. Chlamydia trachomatis
B. Neisseria gonorrhoeae
C. Haemophilus ducreyi
