MICROBIOLOGY FINAL EXAM / ACTUAL EXAM
QUESTIONS AND CORRECT ANSWERS WITH
RATIONALES GRADED A+ LATEST
1. A patient presents with fever, stiff neck, and photophobia. CSF shows high
neutrophils, low glucose, and high protein. Which pathogen is most likely?
A. Neisseria meningitidis
B. Cryptococcus neoformans
C. Mycobacterium tuberculosis
D. Listeria monocytogenes
Answer: A
Rationale: Neutrophil-predominant meningitis with low glucose strongly suggests
acute bacterial meningitis, most commonly N. meningitidis in young adults.
2. Which structure is unique to Gram-negative bacteria?
A. Teichoic acids
B. Thick peptidoglycan
C. Lipopolysaccharide (LPS)
D. Mycolic acids
Answer: C
Rationale: LPS (endotoxin) is found only in the outer membrane of Gram-
negative organisms.
3. A patient develops diarrhea after clindamycin use. What is the best
diagnostic test?
A. Stool culture
B. C. difficile antigen only
C. PCR for toxin genes
D. CSF gram stain
,Answer: C
Rationale: PCR for toxin A/B genes is most sensitive and specific for C. difficile
infection.
4. A wound infection produces a blue-green pigment and a fruity odor. What
microbe is most likely?
A. Proteus mirabilis
B. Pseudomonas aeruginosa
C. Staphylococcus aureus
D. Klebsiella pneumoniae
Answer: B
Rationale: Pseudomonas produces pyocyanin (blue-green pigment) and
characteristic grape-like odor.
5. Which organism is a facultative intracellular pathogen?
A. Staphylococcus epidermidis
B. Listeria monocytogenes
C. Vibrio cholerae
D. Clostridium tetani
Answer: B
Rationale: Listeria survives in phagocytes and spreads cell-to-cell via actin
rockets.
6. A patient with HIV presents with white plaques in the mouth that scrape
off. Which treatment is first-line?
A. Amphotericin B
B. Nystatin oral suspension
C. Fluconazole IV
D. Clotrimazole cream
,Answer: B
Rationale: Oropharyngeal candidiasis (thrush) is treated initially with topical
nystatin.
7. Which bacteria is most associated with biofilm formation on prosthetic
devices?
A. Streptococcus pyogenes
B. Staphylococcus epidermidis
C. Enterococcus faecalis
D. Bacillus anthracis
Answer: B
Rationale: S. epidermidis produces biofilms (polysaccharide matrix) enabling
adherence to prosthetics.
8. Which viral family contains reverse transcriptase?
A. Adenovirus
B. Herpesvirus
C. Retrovirus
D. Reovirus
Answer: C
Rationale: Retroviruses (e.g., HIV) replicate via reverse transcriptase.
9. A patient presents with watery diarrhea after eating undercooked seafood.
Which organism is likely?
A. Vibrio cholerae
B. Shigella flexneri
C. E. coli O157:H7
D. Giardia lamblia
, Answer: A
Rationale: V. cholerae is associated with contaminated water/seafood → profuse
watery diarrhea from ↑cAMP.
10. Which bacterium grows best at 42°C?
A. Campylobacter jejuni
B. Salmonella typhi
C. Vibrio vulnificus
D. Shigella sonnei
Answer: A
Rationale: Campylobacter is thermophilic and prefers 42°C (think: “campfire”).
11. A patient has pneumonia with rust-colored sputum. Which microbe is
likely?
A. Haemophilus influenzae
B. Streptococcus pneumoniae
C. Moraxella catarrhalis
D. Mycoplasma pneumoniae
Answer: B
Rationale: Rust-colored sputum is characteristic of S. pneumoniae.
12. Which organism causes granulomatous inflammation and requires acid-
fast stain?
A. Borrelia
B. Mycobacterium tuberculosis
C. Treponema pallidum
D. Legionella
Answer: B
Rationale: TB forms granulomas and is diagnosed using acid-fast staining.
QUESTIONS AND CORRECT ANSWERS WITH
RATIONALES GRADED A+ LATEST
1. A patient presents with fever, stiff neck, and photophobia. CSF shows high
neutrophils, low glucose, and high protein. Which pathogen is most likely?
A. Neisseria meningitidis
B. Cryptococcus neoformans
C. Mycobacterium tuberculosis
D. Listeria monocytogenes
Answer: A
Rationale: Neutrophil-predominant meningitis with low glucose strongly suggests
acute bacterial meningitis, most commonly N. meningitidis in young adults.
2. Which structure is unique to Gram-negative bacteria?
A. Teichoic acids
B. Thick peptidoglycan
C. Lipopolysaccharide (LPS)
D. Mycolic acids
Answer: C
Rationale: LPS (endotoxin) is found only in the outer membrane of Gram-
negative organisms.
3. A patient develops diarrhea after clindamycin use. What is the best
diagnostic test?
A. Stool culture
B. C. difficile antigen only
C. PCR for toxin genes
D. CSF gram stain
,Answer: C
Rationale: PCR for toxin A/B genes is most sensitive and specific for C. difficile
infection.
4. A wound infection produces a blue-green pigment and a fruity odor. What
microbe is most likely?
A. Proteus mirabilis
B. Pseudomonas aeruginosa
C. Staphylococcus aureus
D. Klebsiella pneumoniae
Answer: B
Rationale: Pseudomonas produces pyocyanin (blue-green pigment) and
characteristic grape-like odor.
5. Which organism is a facultative intracellular pathogen?
A. Staphylococcus epidermidis
B. Listeria monocytogenes
C. Vibrio cholerae
D. Clostridium tetani
Answer: B
Rationale: Listeria survives in phagocytes and spreads cell-to-cell via actin
rockets.
6. A patient with HIV presents with white plaques in the mouth that scrape
off. Which treatment is first-line?
A. Amphotericin B
B. Nystatin oral suspension
C. Fluconazole IV
D. Clotrimazole cream
,Answer: B
Rationale: Oropharyngeal candidiasis (thrush) is treated initially with topical
nystatin.
7. Which bacteria is most associated with biofilm formation on prosthetic
devices?
A. Streptococcus pyogenes
B. Staphylococcus epidermidis
C. Enterococcus faecalis
D. Bacillus anthracis
Answer: B
Rationale: S. epidermidis produces biofilms (polysaccharide matrix) enabling
adherence to prosthetics.
8. Which viral family contains reverse transcriptase?
A. Adenovirus
B. Herpesvirus
C. Retrovirus
D. Reovirus
Answer: C
Rationale: Retroviruses (e.g., HIV) replicate via reverse transcriptase.
9. A patient presents with watery diarrhea after eating undercooked seafood.
Which organism is likely?
A. Vibrio cholerae
B. Shigella flexneri
C. E. coli O157:H7
D. Giardia lamblia
, Answer: A
Rationale: V. cholerae is associated with contaminated water/seafood → profuse
watery diarrhea from ↑cAMP.
10. Which bacterium grows best at 42°C?
A. Campylobacter jejuni
B. Salmonella typhi
C. Vibrio vulnificus
D. Shigella sonnei
Answer: A
Rationale: Campylobacter is thermophilic and prefers 42°C (think: “campfire”).
11. A patient has pneumonia with rust-colored sputum. Which microbe is
likely?
A. Haemophilus influenzae
B. Streptococcus pneumoniae
C. Moraxella catarrhalis
D. Mycoplasma pneumoniae
Answer: B
Rationale: Rust-colored sputum is characteristic of S. pneumoniae.
12. Which organism causes granulomatous inflammation and requires acid-
fast stain?
A. Borrelia
B. Mycobacterium tuberculosis
C. Treponema pallidum
D. Legionella
Answer: B
Rationale: TB forms granulomas and is diagnosed using acid-fast staining.
