-
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
-
What are the 4 phyla of fungi?
- Zygomycota
- Ascomycota
- Basidiomycota
- Deuteromycota
-
Zygomycota - asexual, sexual, hyphae, other
- asexual: sporangiospores
- sexual: zygospores
- hyphae: aseptate or sparsely septate
- other: all spores enclosed within a sporangium (endospores)
-
Ascomycota - asexual, sexual, hyphae
- asexual: conidia
- sexual: ascospores
- hyphae: septate
-
Basidiomycota - asexual, sexual, hyphae, other
- asexual: conidia
- sexual: basidiospores (on basidia)
- hyphae: septate, clamp cells
- other: MUSHROOMS
-
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
-
4 types of mycoses
- superficial cutaneous mycoses
- subcutaneous mycoses
- systemic mycoses (often involve lungs)
- opportunisic mycoses (can become systemic)
-
What is the working schema for IDing fungus
 - dematiaceous: earthy colors, resist dye
- hyaline: nonpigmented, need dye for visualization
-
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
-
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
-
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)
-
SDA (PDA or BHI)
- Sabouraud Dextrose Agar
- Std medium for recovery/maintenance of a wide variety of fungi
- Variations include antibiotics and varying pH
-
IMA
- Inhibitory Mould Agar
- Inhibits bacteria (gentamicin, chloramphenicol)
- Recovers most fungal pathogens (esp Cryptococcus)
-
Blood Culture Media
- Two plated media
- Inhibitory Mold Agar (fungi w/ bacterial inhibition)
- Brain-Heart Infusion Agar (fungi and bacteria)
-
BHI
- Brain-Heart Infusion Agar
- Most fungi, especially from sterile sites (eg. Cryptococcus neoformans from CSF)
- used in yeast-mold conversions (Sporothrix, Paracoccidioides)
- BHI+ gentamycin + chlorampheniol + sheep's blood: recovery of fungi from contaminated spec (eg. Cryptococcus neoformans)
-
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
-
CHROMagar
- Proprietary
- Differential media for Candida spp (diff colors)
-
CMA
- Cornmeal Agar
- Wide range of fungi, particularly fungi imperfecti (Deuteromycota)
- provides balance of mecilial growth and sporulation
-
MEA
- Malt Extract Agar
- Recovery of zygomycetes
- Excellent for environmental cultures
-
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
-
DTM
- Dermatophyte Test Medium
- Recover dermatophytes from heavily contaminated specimens
- Presumptively indicate presence of dermatophytes (turn the medium from pink to red)
-
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
-
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?
-
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
-
How might Dermaophytes look under the scope?
- Freely branching, "antlerlike" apppearance
- Racquet hyphae
- Spiral hyphae
-
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
-
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
-
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
|
|
