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What are mycoses?
What is a hypha?
Structural unit of a fungus
What are pseudohyphae?
Chains of cells formed by budding which resemble true hyphae. They differ from true hyphae by being constricted at the septa.
What is a mycelium?
- Mass of intertwined hyphae.
- Vegetative mycelium or thallus grows into the substrate and absorbs food. It gives color to the back of the culture plate. The aerial or reproductive mycelium projects above the substrate and produces the reproductive cells. It gives color to the front of the culture plate. If growth of aerial mycelia is observed on culture media, the culture must always be handled in a biological safety cabinet.
What are conidia?
Asexual reproductive structures that form on the side or the end of the hypha or conidiophore. Small, single-celled conidia are referred to as microconidia and larger, segmented conidia are referred to as macroconidia.
What are chlamydoconidia (Chlamydospores)?
- Rounded conidia that are thick walled and contain stored food.
- They may be located at the end of the hypha (terminal) or inserted along the hypha (intercalary). Unlike other conidia, they do not readily separate from the hypha.
What are blastoconidia (blastospore)?
A conidium formed by budding along a hypha, pseudohypha, or single cell, as in yeasts.
Name two types of specialized hyphae that bear spores.
- Produce macro and microconidia, and sporangiophores, which produce sporangia
What is a sporangium?
Closed sac-like structure in which sporangiospores are formed
What are arthroconidia (arthrospores)?
Asexual spores formed by the breaking up of a hyphae at the point of septation.The resulting cell may be rectangular or barrel shaped.
What is a yeast?
- Unicellular fungus
- Usually 2.5-6 microns in diameter
- Reproduces by budding
What is a dimorphic fungi?
- One grows as a yeast @ 37 C
- Mold @ Room Temperature
How are most systemic fungal infections contracted?
- Inhalation of spores
- Contamination of a wound with soil
How are skin and nail scraping cleared for microscopic examination for fungal elements?
- Drop of 10% KOH added to specimen on a slide and gently heated.
- KOH dissolves the keratin and makes the fungai more visible.
What is the calcofluor white stain?
- Fluorochrome stain that can be used for rapid screening of clinical specimens for fungal elements.
- Yeast cells, pseudohyphae, and hyphae display a bright apple-green or blue-white fluorescence
Name several media used to culture fungi.
- Sabouraud dextrose agar
- Sabouraud dextrose agar with cycloheximide and chloramphenicol
- Potato dextrose agar
- Inhibitory mold agar
What safety precautions should be taken when molds are isolated in petri dishes?
Lids should be taped to reduce the chance of accidental opening and exposure of infections spores to lab personnel.
At what temperature are fungal cultures incubated and for how long?
- Best temperature is 30 C, but RT is acceptable.
- Cultures left at RT, the ambient temp (22-26 C) must be checked and recorded daily.
- Dimorphic fungus is suspected, it can be subcultured and incubated at 37 C.
- Fungal cultures kept for 1 month.
What is the advantage of a scotch tape prep or a microslide culture over a tease mount?
Spore arrangements are preserved
Which stain is used when examining fungal culture growth microscopically?
- Lactophenol cotton blue. The fungus killed by phenol, preserved by the lactic acid, and stained by the cotton blue.
- Mycelia should always be completely submerged in the stain.
What is the purpose of the India Ink stain?
- Examine CSF when Cryptococcus is suspected. Cryptococcus is a yeast that is surrounded by a wide capsule.
- India Ink prep, halos are seen against a black background. Test is insensitive.
What is ectothrix hair invasion?
Infection in which the fungal elements are located on the outside of the hair shaft.
Which dermatophyte causes hair to fluoresce?
Which fungai commonly cause athletes foot?
Trichophyton mentagrophytes and Trichophyton rubrum
Which fungi cause ringworm of the scalp (tinea capitis)?
- Trichophyton tonsurans is the primary cause of tinea capitis in the US.
- Microsporum audouini used to be the most common cause of tinea capitis in children.
Which dermatophyte produces a colony that is red on the reverse side?
Which pathogenic Candida species is most commonly isolated?
- C. albicans.
- NF of the oral mucosa, skin, and vagina.
- Opportunistic pathogen capable of causing disease in virtually any site.
- Immunocompetent individuals, infections are localized and limited.
- In immunocompromised individuals, C. albicans can disseminate and cause serious infections.
Which fungus produces chlamydospores on cornmeal agar?
- C. albicans, although not all isolates do.
- Chlamydospores are thick-walled spherical cells.
Which yeast causes thrush?
Name a yeast that is urease positive.
Which fungus is recovered from the blood of neonates given lipid replacement therapy and only grows on media overlaid with mineral oil or olive oil?
- Malassezia furfur.
- M. furfur is found on the skin of more than 90% of individuals.
- Systemic infection occurs primarily in neonates and is associated with IV hyperalimentation with lipid solutions.
Describe the microscopic appearance of Malassezia furfur.
- Oval or bottle-shaped budding yeast
- 3-8 microns in diameter with a characteristic collar between mother and daughter cells.
Which fungus produces a white cottony growth on Sabouraud's medium and has barrel-shaped arthrospores?
- Coccidioides immitis
- Causative agent of valley fever. Care must be taken when working with this fungus in the lab because the arthrospores can become airborne and can be inhaled.
Which fungus is hazard to florists and gardeners and is often associated with a rosebush prick (rose gardener's disease)?
Which fungus causes spelunker's disease, found in droppings of pigeons and bats, and has a predilection for the RE system?
With which parasite might Histoplasma be confused.
- LeishmaniaBoth are found in the RE system and morphology similar
Which fungus is associated with severe infections in ketoacidotic diabetics and persons on steroids?
- Microscopic morphology of Mucor is similar to that of Rhizopus, but Mucor does not have rhizoids and the sporangiophores may be branched.