CMLA Microbiology Basics 5

Question 1

Which viral hepatitis is transmitted primarily through the fecal-oral route?

Accepted Answer

Hepatitis A

Answer

Hepatitis A virus (HAV) is transmitted via contaminated food and water (fecal-oral route), unlike hepatitis B and C which spread parenterally.

Question 2

What is the function of a mordant in the Gram staining procedure?

Accepted Answer

Fix the crystal violet–iodine complex to the cell wall

Answer

Gram's iodine acts as a mordant, forming an insoluble crystal violet–iodine complex that becomes trapped within the thick peptidoglycan of Gram-positive cell walls.

Question 3

Clostridium difficile is best detected in stool specimens using which laboratory method?

Accepted Answer

EIA or PCR for toxins A and B

Answer

Enzyme immunoassay (EIA) for C. difficile toxins A/B or PCR-based molecular testing for toxin genes are the preferred diagnostic methods for C. difficile infection.

Question 4

The oxidase test detects the presence of which enzyme in bacteria?

Accepted Answer

Cytochrome c oxidase

Answer

The oxidase test uses a reagent (tetramethyl-p-phenylenediamine) that turns purple when reduced by cytochrome c oxidase, an enzyme in the electron transport chain.

Question 5

Which organism is a common cause of nosocomial (hospital-acquired) urinary tract infections and is known for its characteristic grape-like odor?

Accepted Answer

Pseudomonas aeruginosa

Answer

Pseudomonas aeruginosa produces pyocyanin and has a distinctive grape-like or fruity odor; it is a leading cause of healthcare-associated infections, especially in immunocompromised patients.

(CMLA) Certified Medical Laboratory Assistant Practice Test

(CMLA) Certified Medical Laboratory Assistant Practice Test

CMLA Microbiology Basics 5