Medical Laboratory Technician Exam FREE Medical Laboratory Technician Clinical Microbiology Questions and Answers 2 — Questions and Answers
Question 1: A patient presents with watery diarrhea after recent antibiotic therapy. Which organism is most likely responsible and requires anaerobic culture on selective media?
- Clostridioides difficile (Correct answer)
- Salmonella enteritidis
- Campylobacter jejuni
- Vibrio cholerae
Correct answer: Clostridioides difficile
C. difficile is the leading cause of antibiotic-associated diarrhea and is detected using anaerobic culture on cycloserine-cefoxitin-fructose agar or toxin assays.
Question 2: Which staining technique is most appropriate for identifying Mycobacterium tuberculosis in a sputum specimen?
- Ziehl-Neelsen acid-fast stain (Correct answer)
- Gram stain
- India ink preparation
- Lactophenol cotton blue
Correct answer: Ziehl-Neelsen acid-fast stain
The Ziehl-Neelsen stain uses carbol fuchsin with heat to penetrate the waxy mycolic acid cell wall, rendering acid-fast bacilli red against a blue background.
Question 3: A urine culture grows greater than 100,000 CFU/mL of a Gram-negative rod that is lactose-positive on MacConkey agar and indole-positive. What is the most likely identification?
- Escherichia coli (Correct answer)
- Klebsiella pneumoniae
- Proteus mirabilis
- Pseudomonas aeruginosa
Correct answer: Escherichia coli
E. coli is the most common cause of urinary tract infections and characteristically ferments lactose and produces indole from tryptophan.
Question 4: Which atmospheric condition is required for primary isolation of Campylobacter jejuni from stool specimens?
- Microaerophilic (5% O2, 10% CO2) (Correct answer)
- Strict anaerobic
- Increased CO2 (5-10%) only
- Ambient air at 25 degrees C
Correct answer: Microaerophilic (5% O2, 10% CO2)
Campylobacter jejuni requires a microaerophilic environment with reduced oxygen and elevated CO2, typically incubated at 42 degrees C on selective media.
Question 5: A throat culture on sheep blood agar shows small translucent colonies surrounded by a clear zone of complete hemolysis. Which Lancefield group is most likely represented?
- Group A (Streptococcus pyogenes) (Correct answer)
- Group B (Streptococcus agalactiae)
- Group D (Enterococcus faecalis)
- Non-groupable (Streptococcus pneumoniae)
Correct answer: Group A (Streptococcus pyogenes)
Streptococcus pyogenes (Group A) produces beta-hemolysis on blood agar and is the primary pathogen sought in throat cultures for pharyngitis.
Question 6: Which biochemical test differentiates Staphylococcus aureus from coagulase-negative staphylococci?
- Coagulase test (Correct answer)
- Oxidase test
- Catalase test
- Bile esculin test
Correct answer: Coagulase test
The coagulase test detects the enzyme that clots plasma and is the primary test used to distinguish S. aureus from other staphylococcal species.
