CLS09 - Mycology Overview

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  1. define yeast, mold, dipmorphic
    • yeast: single-celled fungi
    • mold: multicellular fungi
    • dimorphic: having both yeast and mold forms
    • *when this change is dependent on temp. they are thermally dimorphic
  2. What are the 4 phyla of fungi?
    • Zygomycota
    • Ascomycota
    • Basidiomycota
    • Deuteromycota
  3. Zygomycota - asexual, sexual, hyphae, other
    • asexual: sporangiospores
    • sexual: zygospores
    • hyphae: aseptate or sparsely septate
    • other: all spores enclosed within a sporangium (endospores)
  4. Ascomycota - asexual, sexual, hyphae
    • asexual: conidia
    • sexual: ascospores
    • hyphae: septate
  5. Basidiomycota - asexual, sexual, hyphae, other
    • asexual: conidia
    • sexual: basidiospores (on basidia)
    • hyphae: septate, clamp cells
    • other: MUSHROOMS
  6. Deuteromycota - asexual, sexual, hyphae, other
    • asexual: conidia
    • sexual: N/A
    • hyphae: septate
    • other: most clinically significant
    • AKA fungi imperfecti
    • associated w/ Ascomycota, but no sexual repr
  7. 4 types of mycoses
    • superficial cutaneous mycoses
    • subcutaneous mycoses
    • systemic mycoses (often involve lungs)
    • opportunisic mycoses (can become systemic)
  8. What is the working schema for IDing fungus
    • Image Upload 1
    • dematiaceous: earthy colors, resist dye
    • hyaline: nonpigmented, need dye for visualization
  9. Common fungal virulence factors
    • Size of organism (smaller can travel further)
    • ability to grow at 37C at neutral pH
    • conversion from mycelial form to yeast or spherule form in body
    • toxin production
  10. Specimen collection cosiderations for hair, skin, nails, serum, tissue/fluid
    • Hair: 10-12 hairs in clean dry tube/envelope (no stoppers, environment must be dry)
    • room temp
    • Skin: clean w/ 70% EtOH gauze
    • scrape edge of lesion in envelope/vial/between 2 slides
    • room temp
    • Nails: remove polish
    • wipe w/ 70% EtOH gauze
    • collect debris from under nail
    • scrape/discard outer surface of nail
    • sample from deeper diseased nail areas
    • store in envelope, glass vial
    • room temp
    • serum: need both acute and convalescent samples
    • tissue/fluids: sterile, sealed container
    • mince or grind to release
  11. What are the recommended media and "standards" for fungal culture?
    • Plates > screw capped agar: aeration, surface area, ease of handling
    • media: w/ and w/o cycloheximide
    • w/ and w/o antibacterial agent
    • stds: RT (30C)
    • 3wks-6wks (slow)
    • humidity 40-50% (moist)
    • examined a few times each week (too slow to waste time daily)
  12. SDA (PDA or BHI)
    • Sabouraud Dextrose Agar
    • Std medium for recovery/maintenance of a wide variety of fungi
    • Variations include antibiotics and varying pH
  13. IMA
    • Inhibitory Mould Agar
    • Inhibits bacteria (gentamicin, chloramphenicol)
    • Recovers most fungal pathogens (esp Cryptococcus)
  14. Blood Culture Media
    • Two plated media
    • Inhibitory Mold Agar (fungi w/ bacterial inhibition)
    • Brain-Heart Infusion Agar (fungi and bacteria)
  15. BHI
    • Brain-Heart Infusion Agar
    • Most fungi, especially from sterile sites (eg. Cryptococcus neoformans from CSF)
    • used in yeast-mold conversions (SporothrixParacoccidioides)
    • BHI+ gentamycin + chlorampheniol + sheep's blood: recovery of fungi from contaminated spec (eg. Cryptococcus neoformans)
  16. Niger seed agar
    • AKA bird seed agar
    • Differential media
    • C. neoformans colonies appear black/brown (melanin)
    • C. albicans produces only yeast cells while C. dubliniensis produces hyphae and pseudohypahe
  17. CHROMagar
    • Proprietary
    • Differential media for Candida spp (diff colors)
  18. CMA
    • Cornmeal Agar
    • Wide range of fungi, particularly fungi imperfecti (Deuteromycota)
    • provides balance of mecilial growth and sporulation
  19. MEA
    • Malt Extract Agar
    • Recovery of zygomycetes
    • Excellent for environmental cultures
  20. YEP
    • Yeast Extract-Phosphate Medium
    • Enhanced recovery of Blastomyces dermatitidis and Histoplasma capsulatum from contaminated specimens
    • Chloramphenicol inhibits bacteria and drop of NaOH inhibits bacteria/yeasts
  21. DTM
    • Dermatophyte Test Medium
    • Recover dermatophytes from heavily contaminated specimens
    • Presumptively indicate presence of dermatophytes (turn the medium from pink to red)
  22. Direct detection methods (stains) for fungi
    • Gram stains: yeast stain purple/blue (G+)
    • hyphae usually do not stain
    • India ink stain: reveals capsules surrounding C. neoformans esp from CSF
    • KOH: dissolves nonfungal materials
    • Calcofluor white: fluorochrome that stains chitin 
    • Fungi white/blue under ultraviolet light
    • Grocott's methenamine silver: mostly pathology
    • Periodic acid-Schiff: only living fungus, stains magenta
    • Lactophenol cotton blue: wet mount
    • stain/preserve fungal elements
    • *lab staple
  23. What should be looked at on a mold culture?
    • color: front AND reverse
    • topography: verrucose (convoluted), umbonate (raised center), rugose (furrows radiate from center)
    • texture: cottony, granular, wooly
    • temperature: thermally dimorphic?
  24. Various methods of slide preparation
    • Adhesive tape prep: tape used to transfer aerial hyphae from colony to microscopic slide
    • Wet mount: limited use, most common for vaginal secretions
    • tease mount: dissecting needle pulls apart fungal colony which is placed on slide
    • **may damage structure, esp. conidia
    • microslide culture: block of agar overlaid w/ cover slip
    • colonies grown on side of block and onto the slide
  25. How might Dermaophytes look under the scope?
    • Freely branching, "antlerlike" apppearance
    • Racquet hyphae
    • Spiral hyphae
    • Image Upload 2
  26. What are conidia? macroconidia? Microconidia? Arthroconidia, blastoconidia, chlamydoconidia, poroconidia, phialoconidia, annelloconidia?
    • Sporelike asexual reproductive structures produced by the imperfect fungi
    • macroconidia: large and multiseptate
    • microconidia: small and unicellular
    • Arthroconidia: resulting from fragmentation of hyphae into individual cells
    • Blastoconidia: result from budding
    • Chlamydoconidia: terminal hyphael cells that enlarge and have thick walls
    • survive adverse environmental conditions
    • found in molds (chlamydospores in yeasts)
    • Poroconidia: formed by being pushed through small pore in parent cell
    • Phialoconidia: tube-shaped conidia that can be branched
    • Annelloconidia: vase-shaped conidia
  27. Sexual reproduction in fungi requires? Ascospores, Basidiospores, Oospores, Zygospores
    • Requires special structures called spores
    • Ascospores: spores in a saclike structure
    • Basidiospores: spores in a club-shaped structure
    • Oospores: spores from the fusion of cells from two different hyphae
    • Zygospores: spores from the fusion of two identical hyphae
  28. What is the germ tube test?
    • Yeasts incubated w/ serum at 37C for 3 hours and examined for germ tube production
    • (germ tubes are hyphaelike extensions of young yeast cells that are nonseptate and do not constrict at point of origin)
    • C. albicans is positive
    • C. tropicalis is negative
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CLS09 - Mycology Overview
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CLS09 - Mycology Overview
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