Medical Technologist Test Microbiology 1 — Questions and Answers
Question 1: Which culture medium is selective for gram-negative enteric bacteria?
- Blood agar
- Chocolate agar
- MacConkey agar (Correct answer)
- Sabouraud dextrose agar
Correct answer: MacConkey agar
MacConkey agar contains bile salts and crystal violet that inhibit gram-positive organisms while supporting gram-negative growth.
Question 2: A positive catalase test followed by a positive coagulase test identifies which organism?
- Streptococcus pyogenes
- Staphylococcus aureus (Correct answer)
- Enterococcus faecalis
- Listeria monocytogenes
Correct answer: Staphylococcus aureus
Catalase-positive and coagulase-positive results are the key biochemical tests identifying S. aureus among staphylococci.
Question 3: Which stain is used to visualize acid-fast bacilli such as Mycobacterium tuberculosis?
- Gram stain
- India ink
- Ziehl-Neelsen (carbol fuchsin) stain (Correct answer)
- Silver stain
Correct answer: Ziehl-Neelsen (carbol fuchsin) stain
The Ziehl-Neelsen stain uses carbol fuchsin retained by mycolic acid in the cell wall of acid-fast organisms despite acid-alcohol decolorization.
Question 4: Colonies with a green metallic sheen on EMB agar are characteristic of which organism?
- Klebsiella pneumoniae
- Pseudomonas aeruginosa
- Escherichia coli (Correct answer)
- Proteus mirabilis
Correct answer: Escherichia coli
E. coli produces a green metallic sheen on eosin methylene blue (EMB) agar due to strong lactose and acid production.
Question 5: Which organism is the MOST common cause of community-acquired pneumonia in the US?
- Haemophilus influenzae
- Klebsiella pneumoniae
- Streptococcus pneumoniae (Correct answer)
- Legionella pneumophila
Correct answer: Streptococcus pneumoniae
Streptococcus pneumoniae (pneumococcus) remains the leading bacterial cause of community-acquired pneumonia in all age groups.
Question 6: A negative urease test, positive indole test, and positive oxidase test best describes which organism?
- Vibrio cholerae (Correct answer)
- Helicobacter pylori
- Proteus mirabilis
- Enterococcus faecalis
Correct answer: Vibrio cholerae
Vibrio cholerae is oxidase-positive, indole-positive, and urease-negative, distinguishing it from other enteric pathogens.
Medical Technologist Test Microbiology 1
Which culture medium is selective for gram-negative enteric bacteria?