BIOL 271 MICROBIOLOGY WITH LAB
CASE STUDY COMPREHENSIVE QUIZ 1
1. A 19-year-old college student presents with a high fever, severe headache, and nuchal
rigidity. CSF analysis shows Gram-negative diplococci and high neutrophil counts. What is the
most likely pathogen?
A. Streptococcus pneumoniae
B. Listeria monocytogenes
C. Haemophilus influenzae
D. Neisseria meningitidis
Answer: D
Conceptual Explanation: Neisseria meningitidis is a classic cause of bacterial meningitis
in young adults, characterized by Gram-negative diplococci in the CSF.
2. A patient with cystic fibrosis presents with a persistent cough and green-tinted sputum.
The lab isolates a Gram-negative rod that produces a fruity odor and pyocyanin. What is the
organism?
A. Pseudomonas aeruginosa
B. Burkholderia cepacia
,C. Klebsiella pneumoniae
D. Staphylococcus aureus
Answer: A
Conceptual Explanation: Pseudomonas aeruginosa is a common opportunistic pathogen
in cystic fibrosis patients, known for its blue-green pigment (pyocyanin) and grape-like
odor.
3. A 70-year-old patient develops profuse watery diarrhea after a course of clindamycin. Stool
tests are positive for Toxin A and B. Which organism is the causative agent?
A. Salmonella enterica
B. Vibrio cholerae
C. Clostridioides difficile
D. Escherichia coli O157:H7
Answer: C
Conceptual Explanation: C. difficile infection typically follows antibiotic use, which
disrupts normal flora, allowing the toxin-producing bacteria to overgrow.
4. A patient presents with a painful, erythematous skin lesion that is ‘honey-crusted.’
Culturing reveals catalase-positive, coagulase-positive, Gram-positive cocci. Name the
organism.
A. Streptococcus pyogenes
, B. Staphylococcus epidermidis
C. Staphylococcus aureus
D. Propionibacterium acnes
Answer: C
Conceptual Explanation: Staphylococcus aureus is the leading cause of bullous impetigo
and is identified as catalase and coagulase positive.
5. During a routine urinalysis of a sexually active female, the lab finds Gram-positive cocci
that are catalase-positive but coagulase-negative and resistant to novobiocin. Diagnosis?
A. Staphylococcus epidermidis
B. Staphylococcus saprophyticus
C. Enterococcus faecalis
D. Escherichia coli
Answer: B
Conceptual Explanation: S. saprophyticus is a common cause of UTIs in young women
and is uniquely resistant to novobiocin among coagulase-negative staphylococci.
6. A 30-year-old male presents with a painless chancre on his penis. Dark-field microscopy of
the lesion exudate shows motile spirochetes. What is the pathogen?
A. Treponema pallidum
B. Leptospira interrogans
CASE STUDY COMPREHENSIVE QUIZ 1
1. A 19-year-old college student presents with a high fever, severe headache, and nuchal
rigidity. CSF analysis shows Gram-negative diplococci and high neutrophil counts. What is the
most likely pathogen?
A. Streptococcus pneumoniae
B. Listeria monocytogenes
C. Haemophilus influenzae
D. Neisseria meningitidis
Answer: D
Conceptual Explanation: Neisseria meningitidis is a classic cause of bacterial meningitis
in young adults, characterized by Gram-negative diplococci in the CSF.
2. A patient with cystic fibrosis presents with a persistent cough and green-tinted sputum.
The lab isolates a Gram-negative rod that produces a fruity odor and pyocyanin. What is the
organism?
A. Pseudomonas aeruginosa
B. Burkholderia cepacia
,C. Klebsiella pneumoniae
D. Staphylococcus aureus
Answer: A
Conceptual Explanation: Pseudomonas aeruginosa is a common opportunistic pathogen
in cystic fibrosis patients, known for its blue-green pigment (pyocyanin) and grape-like
odor.
3. A 70-year-old patient develops profuse watery diarrhea after a course of clindamycin. Stool
tests are positive for Toxin A and B. Which organism is the causative agent?
A. Salmonella enterica
B. Vibrio cholerae
C. Clostridioides difficile
D. Escherichia coli O157:H7
Answer: C
Conceptual Explanation: C. difficile infection typically follows antibiotic use, which
disrupts normal flora, allowing the toxin-producing bacteria to overgrow.
4. A patient presents with a painful, erythematous skin lesion that is ‘honey-crusted.’
Culturing reveals catalase-positive, coagulase-positive, Gram-positive cocci. Name the
organism.
A. Streptococcus pyogenes
, B. Staphylococcus epidermidis
C. Staphylococcus aureus
D. Propionibacterium acnes
Answer: C
Conceptual Explanation: Staphylococcus aureus is the leading cause of bullous impetigo
and is identified as catalase and coagulase positive.
5. During a routine urinalysis of a sexually active female, the lab finds Gram-positive cocci
that are catalase-positive but coagulase-negative and resistant to novobiocin. Diagnosis?
A. Staphylococcus epidermidis
B. Staphylococcus saprophyticus
C. Enterococcus faecalis
D. Escherichia coli
Answer: B
Conceptual Explanation: S. saprophyticus is a common cause of UTIs in young women
and is uniquely resistant to novobiocin among coagulase-negative staphylococci.
6. A 30-year-old male presents with a painless chancre on his penis. Dark-field microscopy of
the lesion exudate shows motile spirochetes. What is the pathogen?
A. Treponema pallidum
B. Leptospira interrogans
