MYCOLOGY MCQs — Complete Bank REM

Question 1

Amphotericin B would be used to treat all of the following EXCEPT:

Accepted Answer

Valley fever (Coccidioidomycosis) — Ergotism is caused by ergot alkaloids from Claviceps purpurea – this is a toxicosis/poisoning, NOT a fungal infection. Amphotericin B treats fungal infections, not toxin-mediated diseases. All other options are true systemic fungal infections treatable with Amphotericin B.

Question 2

A component of the cell membrane of most fungi is:

Accepted Answer

Ergosterol — Ergosterol is the primary sterol in fungal cell membranes, equivalent to cholesterol in human cells. This difference is clinically significant — most antifungals (polyenes, azoles) target ergosterol specifically, allowing selective toxicity against fungi while sparing human cells. Chitin is a cell wall component, not membrane. Peptidoglycan is bacterial.

Question 3

Which statement regarding dermatophytosis is correct?

Accepted Answer

Acute infections are associated with zoophilic dermatophytes such as M. canis — Zoophilic dermatophytes (animal-adapted, e.g., M. canis) → cause acute, inflammatory infections in humans because humans are a foreign host, triggering a strong immune response. Anthropophilic dermatophytes (human-adapted, e.g., T. rubrum) → cause chronic, low-grade infections because they have adapted to coexist with human immune defenses over time.

Question 4

Which statement regarding laboratory identification of fungi is correct?

Accepted Answer

Since many nonpathogenic molds resemble dimorphic mycotic agents in culture at 30°C, putative dimorphic pathogenic fungi must be confirmed by conversion to tissue form in vitro or by DNA analysis — Since many environmental nonpathogenic molds look similar to pathogenic dimorphic fungi at room temperature, definitive identification requires either converting to yeast form at 37°C in vitro or species-specific DNA sequencing. Important corrections to other options: H. capsulatum takes weeks to culture; the germ tube test identifies C. albicans, NOT C. glabrata; Pneumocystis jiroveci forms cysts and trophozoites, not pseudohyphae.

Question 5

Which of the following is an opportunistic pathogenic fungus in humans?

Accepted Answer

Candida albicans — Candida albicans is part of normal human flora of the mouth, GI tract, and vagina, but causes disease only when host defenses are compromised — making it a true opportunistic pathogen. The others (Blastomyces, Coccidioides, Histoplasma) are primary/true pathogens capable of infecting even immunocompetent hosts when exposed.

Question 6

Aspergillosis is recognized in tissue by the presence of:

Accepted Answer

Septate hyphae — Aspergillus species are identified in tissue by septate hyphae with acute angle (45°) dichotomous branching. This is a critical distinguishing feature from Mucor/Rhizopus which show aseptate (coenocytic) hyphae with wide-angle (90°) branching. This distinction directly impacts treatment choice — aspergillosis uses voriconazole while mucormycosis requires amphotericin B.

Question 7

Fungi often colonize lesions caused by other agents. Which of the following is LEAST likely to be present as a colonizer?

Accepted Answer

Sporothrix — Sporothrix schenckii is a primary pathogen that causes disease exclusively through traumatic inoculation (e.g., thorn prick) — it is NOT an environmental colonizer of pre-existing wounds. In contrast, Candida, Aspergillus, and Mucor are ubiquitous environmental fungi that frequently colonize compromised tissue, wounds, and cavities opportunistically.

Question 8

Each of the following statements concerning Cryptococcus neoformans is correct EXCEPT:

Accepted Answer

Pathogenesis is related primarily to the production of exotoxin A — Cryptococcus neoformans does NOT produce exotoxin A — that is a virulence factor of Pseudomonas aeruginosa. The true virulence factors of Cryptococcus are its polysaccharide capsule (inhibits phagocytosis, impairs complement), melanin production (oxidative defense), and urease (tissue invasion). The capsule is detected by India ink stain and latex agglutination in CSF.

Question 9

Each of the following statements concerning Candida albicans is correct EXCEPT:

Accepted Answer

albicans is transmitted primarily by respiratory aerosol — Candida albicans is NOT transmitted by respiratory aerosol. It is a commensal organism residing in the oral cavity, GI tract, and vagina. Disease arises from endogenous overgrowth when host defenses are disrupted by antibiotics, immunosuppression, diabetes, or pregnancy — not through person-to-person respiratory spread.

Question 10

Natural habitat for Paracoccidioides brasiliensis is:

Accepted Answer

Soil — Paracoccidioides brasiliensis inhabits acidic, humid soil rich in organic matter in Latin America, particularly Brazil. Agricultural workers — especially those working in coffee and tobacco cultivation — are at highest risk due to direct soil exposure and inhalation of airborne spores during soil disruption.

Question 11

Coccidioidomycosis is also called:

Accepted Answer

Valley fever — Coccidioidomycosis is commonly known as "Valley Fever" after the San Joaquin Valley in California, or alternatively "Desert Rheumatism". It is caused by inhaling Coccidioides immitis arthrospores from dry, dusty soil endemic to the southwestern USA and parts of Latin America.

Question 12

One of the most common mycotoxins that infects nuts and grains and causes severe reactions is:

Accepted Answer

Aflatoxins — Aflatoxins produced by Aspergillus flavus and A. parasiticus are the most significant mycotoxins globally, contaminating peanuts, corn, cottonseed, and tree nuts. They cause hepatotoxicity, immunosuppression, and are potent hepatocarcinogens. Critically, they are heat-stable and survive normal cooking temperatures.

Question 13

Coccidioides immitis can exist as molds in soil and spherules in tissues. This characteristic makes it:

Accepted Answer

Dimorphic — Dimorphic means existing in two distinct morphological forms depending on temperature and environment. For C. immitis: mold form at 25°C in soil producing infectious arthrospores, and spherule form at 37°C in tissue producing endospores. This thermal dimorphism applies to all major systemic dimorphic fungi and is a key virulence strategy.

MYCOLOGY MCQs — Complete Bank REM

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