SM Mycology & Fungal Diagnostics 3

Question 1

Candida albicans produces chlamydospores (large, thick-walled spores) when grown on which medium used for morphological identification?

Accepted Answer

Cornmeal agar with Tween 80 at 25–28°C

Answer

Cornmeal agar with Tween 80 induces nutritional deprivation conditions that promote chlamydospore formation in Candida albicans, seen as large, round, thick-walled terminal or intercalary spores on pseudohyphae.

Question 2

The beta-D-glucan assay (e.g., Fungitell) detects which fungal cell wall component as a broad screening test for invasive fungal infection?

Accepted Answer

(1→3)-β-D-glucan

Answer

(1→3)-β-D-glucan is a cell wall polysaccharide present in most clinically significant fungi; the beta-D-glucan assay detects it as a panfungal biomarker, though it is notably absent in Cryptococcus and Mucorales.

Question 3

Which morphological feature is used to microscopically distinguish Aspergillus niger from other Aspergillus species?

Accepted Answer

Biseriate phialides bearing dark brown-black conidia on a large globose conidial head

Answer

Aspergillus niger produces large, biseriate conidial heads with phialides covering the entire globose vesicle, bearing chains of dark brown-black conidia that give colonies their characteristic black appearance.

Question 4

For optimal selective recovery of dermatophytes from skin or nail specimens, Sabouraud dextrose agar should be supplemented with which combination of inhibitory agents?

Accepted Answer

Cycloheximide and chloramphenicol

Answer

Dermatophyte test medium (DTM) and mycosel agar contain cycloheximide (inhibits saprophytic molds) and chloramphenicol (inhibits bacteria), allowing selective isolation of slow-growing dermatophytes from heavily contaminated specimens.

Question 5

Coccidioides immitis and Coccidioides posadasii, the agents of coccidioidomycosis ('Valley Fever'), are endemic to which US geographic region?

Accepted Answer

Arid desert regions of the Southwestern United States

Answer

Coccidioides species are endemic to the arid alkaline soils of the southwestern US (particularly Arizona and the Central Valley of California), where dry conditions favor spore dispersal.

(SM) Specialist in Microbiology Practice Test

(SM) Specialist in Microbiology Practice Test

SM Mycology & Fungal Diagnostics 3