MLT GlobeMycology – page 2
83 Mycology MCQs with answers and explanations.
Branching conidiophores with metulae and phialides bearing chains of conidia, forming a 'brush-like' structure, describe:
The penicillus (brush) of Penicillium consists of branched metulae and phialides without a vesicle. Aspergillus conidiophores end in a swollen vesicle.
A diabetic patient in ketoacidosis has necrotic tissue in the nasal cavity. Histology shows broad, ribbon-like, rarely septate hyphae with right-angle branching. The likely order is:
Rhino-orbital-cerebral mucormycosis in ketoacidosis shows wide, pauciseptate, ribbon-like hyphae branching at wide angles. Aspergillus hyphae are narrow, regularly septate and branch at acute angles.
On cornmeal Tween 80 agar, which feature supports identification of Candida albicans?
Terminal chlamydospores on cornmeal agar with Tween 80 are characteristic of C. albicans (and C. dubliniensis). Arthroconidia suggest Trichosporon or Geotrichum.
A skin scraping from a patient with pale scaly patches on the trunk shows short curved hyphae and round yeasts ('spaghetti and meatballs'). Culture requires olive oil overlay. The organism is:
Malassezia causes pityriasis versicolor, shows the spaghetti-and-meatballs pattern, and most species require lipids for growth. Hortaea causes tinea nigra with dark palmar patches.
Pneumocystis jirovecii in bronchoalveolar lavage is best demonstrated by:
Pneumocystis cannot be cultured routinely; cysts are shown with immunofluorescence, methenamine silver or calcofluor, and PCR is also used. Culture on SDA gives no growth.
Routine fungal cultures for suspected dimorphic pathogens should be held before reporting 'no growth' for at least:
Dimorphic fungi such as Histoplasma and Blastomyces may take several weeks to grow, so cultures are held for about 4 weeks. Shorter holding times risk false-negative reports.
Sabouraud dextrose agar favours the growth of fungi over most bacteria mainly because of its:
The low pH and high sugar content suppress many bacteria while fungi grow well. Cycloheximide is added only in modified formulas and inhibits saprophytic moulds, not bacteria.
Amphotericin B and the azole antifungals act on which component that is found in fungal cell membranes but not in human ones?
Ergosterol is the main fungal membrane sterol; amphotericin binds it and azoles block its synthesis.
Fungal hyphae with regular cross-walls are described as:
Septate hyphae have cross-walls (septa), as in Aspergillus and dermatophytes; Mucorales have mostly aseptate hyphae.
A 'fungus ball' growing inside an old tuberculous lung cavity is usually caused by:
Aspergillus fumigatus commonly colonises existing lung cavities, forming an aspergilloma.
Tinea pedis is commonly known as:
Tinea pedis is dermatophyte infection of the feet; jock itch is tinea cruris and Madura foot is mycetoma.
Dermatophytes infect which tissues?
Dermatophytes use keratin, so they infect only the outer skin, hair and nails.
Cryptococcus neoformans is commonly found in the environment in:
C. neoformans grows well in soil enriched with pigeon droppings; infection follows inhalation.
Fungal infection of the nails is called:
Onychomycosis is nail infection, most often by dermatophytes; otomycosis affects the ear canal.
Routine fungal cultures for moulds are usually incubated at:
Most moulds grow best at 25–30 °C; 37 °C is used additionally to show the yeast phase of dimorphic fungi.
Yeasts such as Candida reproduce asexually mainly by:
Yeasts form buds (blastoconidia) that pinch off from the parent cell.
Aflatoxin, a toxin in poorly stored grains and nuts that can cause liver cancer, is produced by:
A. flavus grows on stored crops and produces aflatoxin, a potent liver carcinogen.
Vaginal candidiasis typically produces a discharge that is:
Candida gives a cottage-cheese-like discharge with itching; frothy discharge suggests Trichomonas and fishy grey discharge suggests bacterial vaginosis.
Candida albicans is best described as:
C. albicans is normal flora of the mouth, gut and vagina and causes disease when defences or normal flora are disturbed.
A mould whose colony is dark brown to black on both the surface and the reverse, due to melanin in its walls, is described as:
Dematiaceous fungi have melanin in their hyphae and conidia; hyaline moulds are colourless or light-coloured.