Molds Practice Questions

Correct answer: Septate hyphae with dichotomous branching at 45-degree angles

Aspergillus is characterized by uniform, septate hyphae that branch at acute angles (approximately 45 degrees). This 'dichotomous' branching pattern is a key diagnostic feature used to differentiate it from Mucorales in histopathology.

Correct answer: Fusarium

Fusarium species are opportunistic pathogens that produce characteristic large, curved, multi-septate macroconidia. They are common causes of mycotic keratitis and can cause disseminated infections in neutropenic patients.

Correct answer: Broad, pauciseptate (aseptate) hyphae

Members of the Order Mucorales possess wide, ribbon-like hyphae with very few or no septa. This structural lack of septation makes the hyphae fragile and prone to collapsing or twisting in clinical specimens.

Correct answer: Rhizopus

Rhizopus species produce root-like structures called rhizoids at the base of the sporangiophore, specifically at the node where the stolon meets the sporangiophore. Mucor species lack rhizoids entirely, which is a primary point of differentiation.

Correct answer: Penicillium

Penicillium species derive their name from the Latin 'penicillus', meaning brush. Microscopically, they show branched conidiophores ending in metulae and phialides that produce long chains of round conidia.

Correct answer: The presence of dark melanin in their cell walls

Dematiaceous (phaeoid) fungi contain melanin in their hyphae and/or conidia, resulting in olive, brown, or black colonies. Examples include Alternaria, Cladosporium, and Curvularia.

Correct answer: Alternaria

Alternaria produces large, dark, club-shaped conidia with cross-walls in two directions (muriform). They often form chains and are common environmental allergens.

Correct answer: Sporangiospores

Molds like Rhizopus and Mucor produce sporangiospores inside a globular sac called a sporangium. When the sporangial wall ruptures, these spores are released into the environment.

Correct answer: Aspergillus flavus

Aspergillus flavus typically produces yellow-green colonies and is a major producer of aflatoxins. Microscopically, its vesicles are often 'circumferential', covered entirely by phialides.

Correct answer: Aspergillus niger

Aspergillus niger grows rapidly and develops a dense layer of black conidia on the surface, giving the colony a peppery appearance. It is a common cause of otomycosis (fungal ear infections).

Correct answer: Aspergillus terreus

Aspergillus terreus is clinically significant because it is often resistant to Amphotericin B therapy. It is identified by its tan to cinnamon colonies and the production of small, round aleurioconidia on its submerged hyphae.

Correct answer: Cladosporium

Cladosporium species produce dark, branching chains of conidia. The cells at the branch points are called shield cells because they possess three attachment scars, resembling a shield.

Correct answer: To suppress rapidly growing saprophytic molds

Cycloheximide is an antifungal agent used to suppress the growth of rapidly growing environmental contaminants. However, it also inhibits several important pathogens like Cryptococcus and many opportunistic molds.

Correct answer: Malassezia furfur

Malassezia furfur is a lipophilic fungus. While it can appear as a yeast, it also forms short hyphae in skin scrapings (the 'spaghetti and meatballs' appearance) and must be cultured on media supplemented with lipids.

Correct answer: Aspergillus

In Aspergillus, the conidiophore terminates in a bulbous swelling called a vesicle. The phialides, which produce the conidia, are attached to this vesicle either directly (uniseriate) or via metulae (biseriate).

Correct answer: Stachybotrys chartarum

Stachybotrys chartarum is a cellulolytic mold that thrives on damp building materials like drywall. It is dark-colored and produces mycotoxins, which have been controversially linked to various health issues in indoor environments.

Correct answer: Trichophyton mentagrophytes

While Trichophyton species are often identified by their microconidia, T. mentagrophytes can produce cigar-shaped or pencil-shaped macroconidia. T. rubrum, by contrast, rarely produces macroconidia and is better known for its 'birds on a wire' microconidia.

Correct answer: Fragmentation of hyphae into rectangular cells

Arthroconidia (or arthrospores) are formed by the simple fragmentation of hyphae. This is a key diagnostic feature for Geotrichum candidum and Coccidioides immitis.

Correct answer: Curvularia

Curvularia conidia are usually four-celled and curved, with one of the central cells being larger and darker than the others. This 'boomerang' or curved shape is highly characteristic.

Correct answer: To kill the fungus for safe handling

In LPCB, Phenol kills the organisms, Lactic acid preserves the structures, and Cotton Blue stains the chitin in the fungal cell walls. This allows for safe and clear microscopic examination.