MLPAO MLPAO Microbiology and Parasitology Diagnostic Methods 5

Question 1

Which colony appearance on Salmonella-Shigella (SS) agar suggests Salmonella?

Accepted Answer

Black-centered colonies on SS agar

Answer

Salmonella is a non-lactose fermenter that produces H2S, giving colorless colonies with black centers on SS agar.

Question 2

Which blood parasite is identified on thin blood film by banana-shaped (crescent) gametocytes?

Accepted Answer

Plasmodium falciparum

Answer

Crescent-shaped gametocytes are characteristic of Plasmodium falciparum.

Question 3

On Kirby-Bauer disk diffusion testing, which factor would most likely produce falsely small zones of inhibition?

Accepted Answer

Inoculum heavier than a 0.5 McFarland standard

Answer

An overly heavy inoculum overwhelms the antibiotic and reduces zone sizes.

Question 4

A CSF India ink preparation shows encapsulated budding yeast. Which organism is most likely?

Accepted Answer

Cryptococcus neoformans

Answer

Cryptococcus neoformans has a polysaccharide capsule that excludes India ink, creating a clear halo.

Question 5

Which test distinguishes Streptococcus pneumoniae from viridans streptococci?

Accepted Answer

Optochin susceptibility and bile solubility

Answer

S. pneumoniae is optochin susceptible and bile soluble, unlike viridans streptococci.

MLPAO - Medical Laboratory Professionals Association of Ontario Practice Test