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.
Medical Laboratory Technician Exam FREE Medical Laboratory Technician Clinical Microbiology Questions and Answers 2
A patient presents with watery diarrhea after recent antibiotic therapy.
Which organism is most likely responsible and requires anaerobic culture on selective media?