Mycology & Virology Lecture Flashcards

A comprehensive set of flashcards covering key concepts, terms, and diagnostic methods from the mycology and virology lecture notes.

What are the general cellular characteristics of fungi (kingdom, cellular organization, and membrane composition)?

Fungi are eukaryotes, achlorophyllous, obligate aerobes with a cell wall made of chitin, glucans, and mannans; their cell membrane contains ergosterol and they require moisture for growth.

How do yeast and mold differ in cellular form and colony appearance?

Yeast are unicellular with moist, creamy, opaque colonies; molds are multicellular with fluffy, cottony, woolly, powdery, or fuzzy colonies. Yeasts reproduce by budding or fission; molds reproduce by spore formation.

Define monomorphic, dimorphic, and polymorphic fungi.

Monomorphic: existing only as yeast or only as mold. Dimorphic: existing as either yeast or mold depending on conditions. Polymorphic: may show both yeast and mold in the same culture (e.g., Exophiala).

What is the fundamental unit of fungi and what is a mycelium?

The hypha is the fundamental unit; a mycelium is a mass of hyphae.

What distinguishes septated from aseptate hyphae, and which group is the exception?

Septated hyphae have cross walls; aseptate (coenocytic) hyphae lack cross walls. Zygomycetes (Mucor, Absidia, Rhizopus) are aseptate; all other fungi are septated.

What do hyaline (moniliaceous) and dematiaceous (phaeoid) fungi refer to?

Hyaline/moniliaceous fungi are colorless or lightly pigmented; dematiaceous fungi are darkly pigmented.

What are spiral hyphae and which organism is associated with them?

Spiral hyphae are coiled hyphal structures; associated with Trichophyton mentagrophytes.

Name the four main types of asexual spores.

Arthroconidia (fragmentation), Blastoconidia (budding), Chlamydoconidia (hyphal enlargement), Sporangiospores (in sporangium); Conidiospores (from conidiophore).

What distinguishes perfect (teleomorph) fungi from imperfect (anamorph) fungi?

Perfect fungi can undergo sexual reproduction; imperfect fungi reproduce asexually or have no known sexual stage.

What are ascospores, zygospores, basidiospores, and oospores?

Ascospores form inside an ascus (ascomycetes); basidiospores form on a basidium (basidiomycetes); zygospores form from the fusion of hyphae; oospores form from differentiated cells in some organisms.

List the common specimen collection guidelines for fungal diagnostics.

Use aseptic technique; avoid swabs for filamentous fungi; process specimens ASAP; refrigeration allowed for short delays; handle skin, hair, nails, blood, CSF, and other specimens appropriately.

Which specimens are examined with Wood’s lamp and what fluorescence patterns help identify them?

Hair samples are examined with Wood’s lamp; Microsporum canis fluoresces yellow-green; Microsporum audouinii fluoresces apple-green.

Name stains used for temporary mounts and what they detect.

KOH mounts (detection of fungal elements); Lactophenol Cotton Blue (preserves/kills and stains fungi); India ink (capsule staining for Cryptococcus); Calcofluor White (fluorescent stain for chitin); PAS and Gomori methenamine silver (GMS) for tissue fungi.

Which stain is used to visualize Cryptococcus neoformans capsule as a clear halo?

India ink (negative stain) shows a clear halo around the capsule.

What stain is used to detect fungal elements with fluorescence of the cell wall?

Calcofluor White, a fluorescent stain for fungal cell wall chitin.

What is the Gomori methenamine silver (GMS) stain used for?

Detects fungi in tissue; fungal elements stain black on a pale background.

What is the Periodic Acid Schiff (PAS) stain used for?

Detects fungi in histological sections by staining polysaccharides magenta.

What is the Niger seed (Birdseed) agar used to detect?

Cryptococcus neoformans pigment production via capsule-related phenotypes.

Which culture medium is selective for dermatophytes and often contains antibiotics?

Sabouraud dextrose agar (SDA) with antibiotics (e.g., chloramphenicol/gentamicin) or Mycobiotic media.

Which medium is used for Aspergillus spp. identification?

Czapek-Dox (Czapek) agar.

Which medium is used for initial isolation of saprophytic fungi and pathogens?

Brain Heart Infusion Agar (BHI), often with antibiotics to suppress bacteria.

Name media used to differentiate Candida spp. by colony color.

CHROMagar Candida; C. albicans green, C. krusei pink/purple, C. tropicalis blue, C. glabrata cream/white.

What test is used as a presumptive identification for Candida albicans?

Germ Tube Test (germ tubes and blastoconidia with chlamydospores).

How does the 42°C growth test help distinguish Candida species?

Candida albicans grows at 42°C; Candida dubliniensis does not grow at 42°C.

What is the 1,3-β-D-glucan (BDG) test used for, and what is an exception to its use?

Pan-fungal marker for invasive fungal infection; exceptions include Cryptococcus neoformans and Mucorales (often negative).

Which test detects Aspergillus antigens in serum?

Galactomannan antigen (often via ELISA).

What assay detects Candida directly in the blood using magnetic resonance?

T2 Magnetic Resonance Assay (T2CM) for Candida directly in blood.

Which genera constitute the dermatophytes?

Microsporum, Epidermophyton, and Trichophyton.

What is Sporotrichosis and its etiologic agent?

Rose Gardener’s disease caused by Sporothrix schenckii; yeast at 37°C (cigar-shaped); mold form with conidia in a flowerette pattern; asteroid body in tissue.

Describe chromoblastomycosis and its key histology.

Chromoblastomycosis (chromomycosis) shows muriform (sclerotic) bodies; copper-colored pigmented fungal cells; “cauliflower” or cauliflower-like lesions.

What is Phaeohyphomycosis?

Infection caused by pigmented (dematiaceous) fungi with pigmented hyphae and/or yeast forms.

What is eumycetoma and how does it present?

Tumor-like deformities caused by fungal infection with granulomatous tissue; may be eumycetoma (fungal) or actinomycetoma (bacterial).

Which organism is associated with rose gardener’s disease?

Sporothrix schenckii.

What is the morphology of Sporothrix schenckii in tissue and in culture?

Yeast at 37°C with cigar-shaped cells; mold form has delicate conidiation on a flower-like arrangement; asteroid body may be seen in tissue.

Name the major opportunistic yeasts.

Candida species (e.g., C. albicans, C. glabrata, C. auris).

What is Cryptococcus neoformans and what capsule feature is diagnostic?

Encapsulated yeast; capsule visualized as a halo with India ink; urease positive; phenol oxidase positive.

Which genus is associated with mold causing aspergillosis (A. fumigatus being common) and who forms a “fungus ball”?

Aspergillus genus; Aspergillus fumigatus is a common pathogen; aspergillosis may form a fungus ball in the lungs of susceptible individuals.

What are the primary diagnostic features of Pneumocystis jirovecii infection?

Cysts are the infective stage; diagnosed by BAL with stains such as Giemsa or Gomori’s methenamine silver showing cysts with punched-out appearance.

What is the difference between dermatophytes’ location and primary infection sites?

Dermatophytes infect keratinized tissues: skin, hair, nails.

Which fungal group is characterized by aseptate (coenocytic) hyphae and lacks cross walls?

Zygomycetes (Mucorales: Mucor, Absidia, Rhizopus).

What are the main systemic mycoses caused by dimorphic fungi?

Blastomyces dermatitidis, Coccidioides immitis, Histoplasma capsulatum, Paracoccidioides brasiliensis; these fungi are dimorphic.

Describe the tissue-form of Histoplasma capsulatum.

In tissue, histoplasma appears within macrophages as small yeasts; mold form has tuberculate macroconidia.

Describe the tissue-form of Blastomyces dermatitidis.

In tissue, forms broad-based budding yeasts; mold form produces lollipobacilloid macroconidia (lollipop-shaped) in culture.

What is the hallmark of Paracoccidioides brasiliensis infection in yeast form?

“Mariner’s wheel” or pilot wheel arrangement of multiple buds around a central cell.

What are Negri bodies and which virus is associated with them?

Negri bodies are eosinophilic inclusion bodies in neurons; associated with Rabies virus (Rhabdoviridae).

Which viruses are encapsulated and known for latency in humans (Herpesviridae)?

Herpesviridae family; includes HSV-1, HSV-2, VZV, EBV, CMV, HHV-6/7, HHV-8 with latent infections.

What is the Dane particle?

The infectious virion form of hepatitis B virus (Hepadnaviridae); associated with carrier state.

Which virus family includes HPV and what are the high-risk types associated with cancer?

Papillomaviridae; high-risk types include HPV-16 and HPV-18 (cervical cancer risk); others (e.g., HPV-11, 6) are more associated with warts.

Which poxviruses are notable and what are their roles?

Variola (smallpox) caused by Variola virus; Vaccinia is used in smallpox vaccination; Molluscum contagiosum virus causes molluscum contagiosum; Orf virus is zoonotic; Monkeypox is a zoonotic poxvirus.

Name common RNA virus families that cause human disease (examples).

Orthomyxoviridae (influenza), Paramyxoviridae (measles, mumps, RSV, PIV), Flaviviridae (dengue, yellow fever, Zika, West Nile), Togaviridae (rubella, chikungunya); Caliciviridae (norovirus), Astroviridae (astrovirus).

What is the characteristic of coronaviruses in terms of structure and detection?

Coronaviridae have enveloped RNA viruses with crown-like spikes; detected by nucleic acid tests and electron microscopy; include SARS-CoV, MERS-CoV, SARS-CoV-2.

What is the hallmark of antigenic drift vs antigenic shift in influenza?

Drift: gradual, partial mutations causing local outbreaks; Shift: major reassortment leading to pandemics.

Which receptor does SARS-CoV-2 use to enter host cells?

ACE2 (angiotensin-converting enzyme 2) receptor.

What is the primary diagnostic method for many non-culturable viruses?

Molecular nucleic acid tests (NAATs) such as RT-PCR or PCR; serology for past exposure; sometimes antigen tests.

Which technique is considered the gold standard for immunofluorescence in virology?

Immunofluorescence (IF) is a gold standard for detecting viral antigens using labeled antibodies.