AP-Micro Microbiology: Mycology and Parasitology 3 — Questions and Answers
Question 1: Cryptococcus neoformans is distinguished from other pathogenic fungi by its:
- Ability to form germ tubes at 37°C
- Large polysaccharide capsule visible with India ink stain (Correct answer)
- Production of aflatoxin B1
- Formation of arthroconidia in dry environments
Correct answer: Large polysaccharide capsule visible with India ink stain
The large polysaccharide capsule of C. neoformans is its hallmark virulence factor and is visualized as a clear halo around cells using India ink staining of CSF.
Question 2: Which parasite is transmitted by the bite of a female Anopheles mosquito?
- Trypanosoma brucei
- Plasmodium vivax (Correct answer)
- Leishmania donovani
- Wuchereria bancrofti
Correct answer: Plasmodium vivax
All four Plasmodium species causing human malaria are transmitted exclusively by the bite of infected female Anopheles mosquitoes.
Question 3: Coccidioidomycosis is endemic to which geographic region of the United States?
- Great Lakes region
- Southwestern deserts (San Joaquin Valley) (Correct answer)
- Appalachian highlands
- Gulf Coast wetlands
Correct answer: Southwestern deserts (San Joaquin Valley)
Coccidioides immitis thrives in the hot, dry soils of the Southwestern US (especially California's San Joaquin Valley and Arizona), where its arthroconidia become airborne.
Question 4: Giardia lamblia trophozoites are characteristically distinguished by their:
- Single nucleus and large food vacuole
- Two nuclei and ventral adhesive disc (Correct answer)
- Undulating membrane and single flagellum
- Amoeboid pseudopodia and no flagella
Correct answer: Two nuclei and ventral adhesive disc
Giardia trophozoites have two nuclei giving a 'face-like' appearance and a ventral sucking disc used to adhere to intestinal epithelium.
Question 5: The primary antifungal mechanism of amphotericin B is:
- Inhibition of β-1,3-glucan synthase in the cell wall
- Binding to ergosterol and forming pores in the fungal membrane (Correct answer)
- Blocking fungal DNA synthesis by inhibiting topoisomerase
- Inhibiting lanosterol 14α-demethylase in the ergosterol pathway
Correct answer: Binding to ergosterol and forming pores in the fungal membrane
Amphotericin B binds directly to ergosterol in the fungal cell membrane, forming channels that cause potassium leakage and cell death.
Question 6: Schistosoma mansoni infection is acquired by:
- Ingesting undercooked freshwater fish containing metacercariae
- Skin penetration by cercariae released from freshwater snails (Correct answer)
- Ingesting cysts on contaminated vegetables
- Bites from infected blackflies (Simulium species)
Correct answer: Skin penetration by cercariae released from freshwater snails
Schistosome cercariae are released from infected Biomphalaria snails into freshwater and directly penetrate human skin during contact with contaminated water.
Question 7: Pneumocystis jirovecii pneumonia (PCP) is best diagnosed by:
- Blood culture on Sabouraud dextrose agar
- Microscopic visualization of cysts in induced sputum or BAL using GMS stain (Correct answer)
- Serum galactomannan assay
- Urine antigen lateral flow assay
Correct answer: Microscopic visualization of cysts in induced sputum or BAL using GMS stain
P. jirovecii cannot be cultured; diagnosis relies on visualizing cysts in respiratory specimens using Gomori methenamine silver (GMS) or immunofluorescence staining.
AP-Micro Microbiology: Mycology and Parasitology 3
Cryptococcus neoformans is distinguished from other pathogenic fungi by its: