Fungi - Kinzy 5/11/16 Flashcards
fungi
general characteristics
- eukaryotes
- good bc all of the info we have about human n.a./protein synthesis applies
- bad bc makes selective targeting difficult
- thick rigid walls (barrier)
- ergosterol instead of cholesterol in membranes (target of many tx)
- saprophytic
- spore-formers
- potent immunogens (source of many allergies)
- susceptible: neutropenic patients (cancer, organ transplant)
why is prevention of fungal infection better than tx?
5 classes of anti-fungal drugs with ex
drug cadre is very small, often with lousy side effects
- 5-fluorocytosine : converted to FdUMP (dTMP analogue) - TOXIC
- membrane inhibitors : polyenes : bind ergosterol, disrupt membrane
- nystatin (toxic; for topical use only)
- amphotericin (for systemic inf; bad side effects)
- azoles : inhibit ergosterol synthesis
- pentamidine : specific for Pneumocystis
- echinocandins (caspofungin) : inhibit cell-wall glucans synth
classification of fungi
dependent on structures in which meiosis takes place (requires starvation, specific conditions - rarely seen in clinical situations)
4 groups:
- zygomycetes
- ascomycetes
- basidiomycetes
- fungi imperfecti (no meitotic stage)
zygomyces
growing forms fuse → sporangium (in which multiple nuclei undergo meiosis)
ascomyces
4 or 8 meiotic spores in a sac (ascus)
how?
- diploid nucleus goes through meiosis → 4 haploid nuclei, go through mitosis → 8 haploid nuclei
- old cell wall forms sac around
- if sac breaks, spores released into environment
basidiomycetes
conidia (sexual spores) bud from basidium (club-shaped terminal cell of hypha)
fungi imperfecti
not sure if truly asexual or if conditions under which meiotic stage occurs just have yet to be found
clinical material is always “imperfect”/asexual form
fungi ID in lab
culture : typically not fastidious, can grow in general media
- Saboraud agar: broth-based + glucose
pigmentation : dermaticiaceous (pigmented) vs. hyaline (colorless)
size : bigger than bacteria!
important : morphology, site of infection
- site can inform tx
serology not that important because we contain lots of antibodies to fungi due to common prior infections
terminology: [no reverse card]
elongation of fungal cells : hyphae
mass of hyphae : mycelium
yeast vs mold vs pseudohyphae vs etc
yeast:
- single cells, growth by budding
- smooth, creamy colonies in culture
mold:
- cells elongate, form hyphae → mycelia
- large, fuzzy colonies; often pigmented
pseudohyphae:
- yeast buds elongate but do not separate
chlamydospores:
- large round terminal cells with thick walls (also pseudohyphae, microconidia)
conidia:
- thick-walled resting/dispersal stage
- microconidia are small
- macroconidia have cross-walls (septae)
- arthroconidia : alternate cells have thick walls, later hyphae break apart at septa
- phiaoloconidia : chains of conidia bud from specialized terminal cells of hyphae
fungal infections by location
superficial : outermost layer of skin, hair
- fungi digest keratin
cutaneous : confined to skin or mucous membranes
subcutaneous : deeper tissues
systemic : often start in lungs → dissemination
Piedra
caused by Trychophyton (dermatphyte)
superficial inf of hair
hyphae grow in hair shaft
tinea
superficial infections of skin caused by…
- Trichophyton
- Epidermophyton
- Microsporum
distinguished by micro/macroconidia
clinical/dx: lesion with inflamed rim of active infection + central clearing
- get specimen from RIM
source: soil, animals, humans; more common in hot, humid climate
different tineas
tinea corporis : body : “ringworm”
tinea capitis : head : fluorescent under UV (Wood’s lamp)
tinea barbae : beard area
tinea pedis : athlete’s foot
tinea unguis : onychomycosis (nails)
subcutaneous mycoses
fungi introduced by local trauma → formation of abscesses or mycetoma (“fungal tumor”)
**similar lesions can also be produced by bacteria Actinomycetes
