ASCP Microbiology 1 — Questions and Answers
Question 1: Which organism is the most common cause of community-acquired urinary tract infections?
- Klebsiella pneumoniae
- Staphylococcus saprophyticus
- Escherichia coli (Correct answer)
- Enterococcus faecalis
Correct answer: Escherichia coli
Escherichia coli accounts for approximately 80–85% of community-acquired urinary tract infections.
Question 2: A Gram stain showing gram-positive cocci in clusters is most consistent with:
- Streptococcus pneumoniae
- Staphylococcus species (Correct answer)
- Enterococcus faecalis
- Listeria monocytogenes
Correct answer: Staphylococcus species
Staphylococci characteristically appear as gram-positive cocci in grape-like clusters on Gram stain.
Question 3: Which test differentiates Staphylococcus aureus from coagulase-negative staphylococci?
- Catalase test
- Coagulase test (Correct answer)
- Oxidase test
- Urease test
Correct answer: Coagulase test
S. aureus produces coagulase, which clots plasma, while coagulase-negative staphylococci (e.g., S. epidermidis) do not.
Question 4: Which medium is selective for gram-negative enteric pathogens like Salmonella and Shigella?
- Blood agar
- Chocolate agar
- Hektoen enteric (HE) agar (Correct answer)
- Thayer-Martin agar
Correct answer: Hektoen enteric (HE) agar
Hektoen enteric agar inhibits gram-positive bacteria and differentiates enteric pathogens by lactose fermentation and H2S production.
Question 5: The CAMP test is used to identify which organism?
- Listeria monocytogenes
- Streptococcus agalactiae (Group B Strep) (Correct answer)
- Clostridium perfringens
- Corynebacterium diphtheriae
Correct answer: Streptococcus agalactiae (Group B Strep)
Group B Streptococcus produces the CAMP factor that enhances beta-hemolysis of S. aureus, creating an arrowhead zone.
Question 6: Which fastidious organism requires X (hemin) and V (NAD) factors and causes meningitis in children?
- Neisseria meningitidis
- Haemophilus influenzae (Correct answer)
- Streptococcus pneumoniae
- Listeria monocytogenes
Correct answer: Haemophilus influenzae
Haemophilus influenzae requires both hemin (factor X) and NAD (factor V) for growth and was a major cause of pediatric meningitis before vaccination.
ASCP Microbiology 1
Which organism is the most common cause of community-acquired urinary tract infections?