ASCP Microbiology 3

Question 1

Viridans streptococci cause which serious infection by colonizing damaged heart valves?

Accepted Answer

Bacterial endocarditis

Answer

Viridans streptococci are the most common cause of subacute bacterial endocarditis, particularly in patients with pre-existing valvular disease.

Question 2

Which parasite is identified by finding trophozoites with ingested red blood cells in stool?

Accepted Answer

Entamoeba histolytica

Answer

Entamoeba histolytica trophozoites actively ingest red blood cells (erythrophagocytosis), a pathognomonic finding in stool.

Question 3

The KOH preparation of skin scrapings showing hyphae and yeast ('spaghetti and meatballs') is diagnostic of:

Accepted Answer

Tinea versicolor (Malassezia furfur)

Answer

Malassezia furfur, the cause of tinea versicolor, produces characteristic short hyphae and round yeast cells resembling spaghetti and meatballs.

Question 4

Stool culture for cholera (Vibrio cholerae) uses which selective medium?

Accepted Answer

TCBS (thiosulfate-citrate-bile salts-sucrose) agar

Answer

TCBS agar selects for Vibrio species; V. cholerae ferments sucrose producing yellow colonies on this medium.

Question 5

Which test is used to detect penicillin susceptibility differences between S. pneumoniae isolates?

Accepted Answer

1-µg oxacillin disk diffusion or MIC testing

Answer

The 1-µg oxacillin disk screens for penicillin-non-susceptible pneumococci; MIC testing then determines exact susceptibility categories.

ASCP Practice Test