Untitled Quiz

Physiological Tests for Fungi

• Glucose, melibiose, D-glucitol are positive for Malassezia furfur.
• L-rhamnose and D-glucitol are negative for Trichosporon inkin.
• Galactose, raffinose, α-methyl-D-glucoside are positive for Trichosporon inkin.
• L-sorbose, melezitose, N-acetyl-D-glucosamine, D-gluconate are mostly positive for Trichosporon inkin.
• Sucrose, soluble starch, glycerol, DL-lactate are mostly negative for Trichosporon inkin.
• Maltose, D-xylose, erythritol are positive for Trichosporon inkin.
• Cellobiose and L-arabinose are positive for Trichosporon inkin.
• Ribitol and nitrate are negative for Trichosporon inkin.
• Trehalose, D-arabinose, galactitol are positive for Trichosporon inkin.
• 2-keto-D-gluconate is negative for Trichosporon inkin.
• Lactose, D-ribose, and D-mannitol are positive for Trichosporon inkin.
• D-glucuronate is positive for Trichosporon inkin.

Malassezia furfur

• Also known as Tinea versicolor, Pityriasis versicolor, Dermatomycosis furfuracea, tinea flava, chromophytosis.
• Colonies are restricted, white, finely cerebriform with a granular covering, without a marginal zone, often cracking the media; yellow to brown color species.
• Laboratory diagnosis involves KOH/PAS preparation of skin scrapings.

Trichosporon spp. vs. Aspergillus spp.

• Trichosporon spp. have correctly formed septate tissue; Aspergillus spp. do not.
• Trichosporon spp. have a low disease-causing ability; Aspergillus spp. have high disease-causing ability.
• Penicillium spp. are commonly used in antibiotic production; Aspergillus spp are not popular in antibiotic production.

Rhizopus (Bread Mold)

• Specimen for diagnosis: sputum, urine, scrapings from lesions, bone marrow biopsy, skin, lymph nodes.

Histoplasma capsulatum

• Morphology: microscopic small, ovoid cells intracellularly in histologic sections; stained with Gomori methanamine silver or Giemsa stain.
• Macroconidia: thick-walled, spherical structures (8-15 μm diameter) with surface projections.
• Microconidia: smooth, spherical structures (2-4 μm diameter).
• Disease: Histoplasmosis.
• Miscellaneous tests: serological tests (immunodiffusion, latex agglutination test).
• Mode of transmission: inhalation of conidia.
• Pathogenesis: intracellular mycosis of the reticuloendothelial system; infection is self-limited; symptoms include fever, chills, myalgias, headaches, non-productive cough; severe disseminated histoplasmosis involves the reticuloendothelial system with lymphadenopathy, enlarged spleen, liver, high fever, and anemia.
• Treatment: Amphotericin B.
• Colony characteristics (SDA): white to tan cottony colonies; pale yellow-brown on reverse.

Coccidioides immitis

• Disease: Coccidioidomycosis.
• Mode of transmission: inhalation of airborne arthroconidia.
• Pathogenesis: infection is self-limited; dissemination is rare but may be fatal.

Blastomyces dermatitidis

• Patients with primary infection are often asymptomatic.
• Symptoms: fever, malaise, cough, headache.
• Late-stage patients may have hypersensitivity reactions such as erythema nodosum or erythema multiforme (rashes).
• Specimen for diagnosis: sputum, pus, CSF, tissue biopsy material.
• Morphology: microscopic spherule with thick, doubly refractile wall; endospores form within the spherule and fill it.
• Macroconidia: globose (8-15 μm) with distinctive tuberculate or finger-like cell wall ornamentation.
• Microconidia: ovoid (2-4 μm), smooth or finely roughened.
• Miscellaneous tests: serological tests (immunodiffusion, latex agglutination test).
• Macroscopic morphology (22°C): slow to moderate growth; white to dark tan young colonies, tenacious; old colonies glabrous to wooly.
• Microscopic morphology (22°C): oval, pyriform to globose smooth conidia borne on short, lateral hypha-like conidiophores.
• Microscopic morphology (BAP at 37°C): large yeast (8-12 μm); blastoconidia attached by broad base; small, oval yeast (2-5 μm).
• Colony characteristics (SDA): white to tan colony.

Paracoccidioides brasiliensis

• Macroscopic morphology (22°C): slow growth; white to beige colony; glabrous, leathery, flat to wrinkled, folded, or velvety.
• Microscopic morphology (22°C): colonies frequently produce only sterile hyphae; fresh isolates may produce conidia similar to those of Blastomyces dermatitidis.

Phialophora verrucosa

• Type of mycosis: subcutaneous.
• Causative agent of chromoblastomycosis: verrucous nodules that often become ulcerated and crusted.
• Diagnosis: presence of characteristic lesions accompanied by microscopic sclerotic bodies (copper pennies).
• Macroscopic morphology: dry, smooth or lightly wrinkled, glistening or dull.
• Microscopic morphology: presence of collarettes during conidiogenesis.

Unidentified Fungus (Likely Malassezia sp.)

• Wood's lamp fluorescence: golden yellow to light green fluorescence in lesions/hair.
• Microscopic examination (KOH): round budding yeast cells with hyphae.
• Microscopic examination (PAS): "spaghetti and meatball appearance".
• Culture (SDA): must be overlaid with olive, peanut, or vegetable oil due to lipophilic nature; colonies are shiny, moist, yeast-like, dirty white-brown coloration, eventually turning olive to greenish black.
• Microscopic examination (young cultures): budding blastoconidia.
• Microscopic examination (old cultures): clusters of blastoconidia.
• Microscopic examination (older hyphal colonies): annelloconidia.