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Mycology
Week 4
19
Veterinary Medicine
Graduate
07/14/2015

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Term
Mycology
Definition
Uni or multicellular organisms
Aerobic eukaryotes
Defined nuclei
Cell walls of carbohydrate and chitin, ergosterol in plasma membrane
Saprophytic or parasitic
Sexual and asexual reproduction
Asexual spores by mitosis – infectious forms of hyphal fungi
Term
Lab Diagnosis of Fungal Infection
Definition
Clinical specimens
Direct microscopy – KOH preps, calcofluor white, Gram stain on colonies, Giemsa
Culture – Sabarauds dextrose agar, chromagar, specialised agars - days or weeks
Identification by morphology of hyphae, production of spores
PCR
Histology of tissue in invasive disease – silver stains
Term
Yeast
Definition
Unicellular organisms that reproduce by budding - grow on skin, mucous surfaces and in the body
Some times daughter cells may not detach themselves - the result is a pseudohyphae (pseudo and true hyphae – Candida albicans)
Term
Moulds
Definition
Filamentous hyphal fungi
Multicellular, multinucleate
Basic unit is the hyphae, a long thin filament
Hyphae branch and cross link to forma mat (mycelium)
Growth occurs at hyphal tip
Hyphae may be divided by cross-walls (septa) into uninuclear units
Non septate hyphae: coenocytic
Septa contain pore. All cytoplasm is connected.
Term
Dimorphic Fungi
Definition
Organisms that can produce both hyphae and yeast-like forms. Moulds in the environment, yeast in animal tissue – yeast is the pathogenic form
Term
Candida
Definition
Gram positive. Yeasts, pseudohyphae.
Grows at 37C on Sabouraud’s dextrose agar/Chromogenic agar
Creamy white 2mm colonies
Term
Candida albicans
Definition
Cattle - Mycotic abortion, Rumenal infections, Mastitis
Pigs - dermatitis
Dogs - chronic enteritis and dermatitis, vaginitis/vulvitis in diabetes
Birds - crop infections, enteritis
Man – mucosal and systemic infection
Term
Malassezia
Definition
Yeast
Bottle shaped
Malassezia pachydermatis
Grows on Sabouraud’s dextrose agar at 37C
Lipase, urease
Otitis externa, Dermatitis
Term
Cryptococcus
Definition
Yeast
C. neoformans, C. grubii, C gattii
Inhalation of yeast cells in dust – pigeon faeces
Opportunistic infections – defective cell mediated immunity - meningitis
Nasal cavity of cats with chronic rhinitis
Nasal, cutaneous, neural and ocular disease in cats
Mucilaginous capsule – india ink stain – virulence factor
20 m total
Term
Dermatophytes
Definition
Microsporum, Trichophyton sp.
Digest keratin – infect skin, hair and nails
Term
Microsporum
Definition
mould
RINGWORM
Dermatophyte
M. canis
M. gypseum
M. nanum
May fluoresce under Wood’s light
Term
Trichophyton
Definition
mould
RINGWORM
Dermatophyte
Spiral hyphae
No fluorescence
T. verrucosum - cattle
T. mentagrophytes - dog, horse
T. equinum - horse
T. gallinae - fowl
Term
Aspergillus
Definition
mould
A. fumigatus - on food stuff
Mainly respiratory infection
Term
Histoplasma capsulatum
Definition
Endemic in Mississippi and Ohio river valleys
Man, Dogs and cats
Impaired CMI
Granulomas in lungs
Infection of macrophages
Term
Zygomycetes
Definition
Broad hyphae non-septate
Asexual spores in a sporangium
Sexual spores oospores or zygospores
Mucor, Rhizopus, Absidia, Saprolegnia
Infection uncommon in healthy immunocompetent animals
Immunodeficiency, steroids, antibiotics
Abortion in cattle
Rumenitis
Term
Mycotoxins
Definition
Secondary metabolites of fungal species in crops, pasture or stored feed
Term
Aflatoxin
Definition
Difuranocoumarins – Aspergillus sp. Aflatoxicosis – absorption from GI tract, metabolised by liver to toxic product – carcinogenic
Term
Ergotism
Definition
Ergopeptide alkaliods – Claviceps purpurea – domestic animals and humans – seed heads of grasses and cereals – ergotamine and ergometrine – affect nerves supplying arteriolar smooth muscles
Term
Mycotic oestrogenism
Definition
Zearalenone – potent non steroidal oestrogen produced by Fusarium sp. – maize other cereals – reproductive problems in cattle and sheep
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