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Flashcards in Fungi Deck (31)
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1

Fungi- general characteristics

Uni (yeast) or multicellular organism
Aerobic eukaryotes
Defined nuclei
Cell walls of CHO and chitin- ergosterol in plasma membrane
Saprophytic or parasitic
Sexual and asexual repro
Asexual spores by mitosis- only found in clinical infection, no sexual reproduction in clinical infection.

2

Fungi definition

Fungi: all yeasts, yeast-like organisms, dimorphics and moulds.
Yeasts: unicellular organisms that reproduce by budding- grow on skin, mucous surfaces and in the body- commensals, but can be pathogenic
Moulds: multicellular organisms that produce hyphae and mycelium (individual strains of hyphae) and spores (e.g. dermatophytes- hyphae grow in skin, hair and nails)
Dimorphic fungi: organisms that can produce both hyphae and yeast-like forms. Hyphae in environment (+spores) and yeasts in the infected host- geographically restricted.
-exhibit temperature dimorphism

3

Fungi in veterinary medicine

Cutaneous and superficial mucous membranes- dermatophytes, malessezia, candida
Subcutaneous (rarest form)
Systemic: primary pathogens (histoplasma)- cause infection in healthy animals; opportunistic pathogens (aspergillus- disease causing in immunocompromised)
Toxins: mycotoxins
Allergy: to fungal spores

4

Fungal benefits and pitfalls

Fungal products: ABX and mycotoxins (some are carcinogenic)
Fungal spoilage: animal foods, forages, animal products such as meat and hides

5

Yeasts- general characteristics

single cells, reproduce vegetatively by budding
occasionally form pseudo mycelium (pseudo and true hyphae)- candida in particular do this
Sexual reproduction by forming ascospores within cell- only in nature, not in infected animal
Candida, malassezia, cryptococcus

6

Candida- general characteristics

MUCH larger than bacteria, gram stain positive
yeasts, pseudohyphae, hyphae in tissue
chlamydospores- thick walled resting spores
grow at 37 degrees
form creamy white 2mm colonies in around 18 hours

7

Candida albicans in animal disease

Cattle: mycotic abortion, rumenal infections, mastitis- may be superimposed after bacterial mastitis. ABX treatment will clear normal flora--> superimposed candida albicans infection
Pigs: dermatitis
Dogs: chronic enteritis and dermatitis, vaginitis/vulvitis in diabetes (yeast can use sugar present in tissues)
Birds: crop infection, enteritis
Man: mucosal and systemic infection

8

Malassezia

skin commensals normally
bottle shaped
M. pachydermatis
Contain lipase and urease- break down lipid-->inflamm reaction
Otitis externa in dogs mainly
Dermatitis in all species- particularly dogs and cats

9

Cryptococcus

C. neoformans, C. grubii, C. gatti
Inhalation of yeast cells in dust- pigeon feces
Opportunistic infections- defective cell mediated immunity, meningitis
Nasal cavity of cats with chronic rhinitis
Causes nasal, cutaneous, neural and ocular disease in cats.
Mucilagenous capsule- virulence factor

10

Dermatophytes-microsporum, trichophyton sp.

Septate branching hyphal fungi
3 classes: anthrophilic (human-human), geophilic (enviro to animal/human), zoophilic (animal to human)
Digest keratin: hall mark- infect skin, hair and nails
Infectious spores=arthrospore
Form microconidia and macroconidia
Grow on sabouraud's within 7-14 days, but up to 4 weeks.

11

Ectothrix/endothrix

ectothrix- when you pluck hair, spores on the outside
endothrix- spores inside hair shaft

12

Microsporum

ringworm in man and animals- looks like a cutenous parasitic infection.
Anthropophilic, zoophilic and geophili
Microconidia en thryse (along sides of hyphae)
Diagnosis by fluorescence under long wave UV light

13

Microsporum canis

Ringowrm in cats and dogs-- transmissible to man
Grows on hair with arthrospores- ectothrix
Micronidia relatively common
Macrocondiai elliptical with up to 14 divisions (canoe shaped)
Fluoresces
Colonies smooth white surface, yellow underside
Hair loss, skin inflammation, itchiness, scaly lesions

14

Other microsporum species

M. gypseum- many macroconidia, dog, geophilic- associated with hedgehogs (doesn't fluorescence)
M. nanum- pigs (not UK)- tropical disease

15

Trichophyton

Zoophilic, ringworm in man and animals
club-shaped macroconidia
-microconidia(en thryse and en grappe)
spiral hyphae
no fluorescence of lesions

16

T. verrucosum

ringworm in cattle transmissible to man
abundant chalmydospores- produced in culture only
-large spore ectothrix on hair
colonies slow growing- up to 8 weeks
embed themselves deep in agar

17

Other species of tricophyton

T. mentagrophytes- dog, horse
-cigar shaped macroconidia, spiral hyphae
T. equinum- horse
T. galinae- fowl

18

Aspergillus

not skin pathogens, respiratory, systemic opportunistic pathogens
Septate branching hyphae
sporing heads or conidia in O2
conidiophore and sterigmae
morphology of heads and culture which allows for diagnosis

19

Aspergillus fumigatus

commonest in humans and animals
on food, fodder
sores infect young, non-immune or immunosuppresesed animals (also if you have A LOT of spores)
star shaped colonies
green-blude with sporing heads
need histopath evidence and culture to confirm

20

Aspergillus disease

mainly respiratory infection- spore inhalation
pneumonia in newly hatched chicks
air sacculitis in birds- severe disease
guttural pouch mycosis in horses
nasal aspergillosis in dogs- particularly if on steroids
Mycotic abortions in cows- poor quality feed
Man- allergic diseases and severe infection in immunocompromised.

21

Host defenses against aspergillus- lung

inactive conidia are inhalaed--> conidia lodge in lower respiratory tract--> conidia swell--> blocked by macrophages (in healthy animal hyphae prevented from forming)
If macs can't block, conidia germinate into hyphae. Can be blocked by neutrophils. If not blocked, hyphae invade tissues. Can be blocked by neutrophils. If not blocked by neutrophils, hyphae invade BVs and disseminate.
Aspergillus have tropism for BVs--> like to go to brain.

22

Dimorphic fungi

Geographically restricted (not in UK)
2 distinct forms: mould and yeast
Moulds in the environment, yeast in animal tissue (pathogenic)
Moulds produce spores--> spores inhaled or introduced into the skin
Species most associated: histoplasma capsulatum, blastomyces dermatitis, coccidioides immitis and sporothrix schenkii (subcut)

23

Histoplasma capsulatum

Endemic in Mississippi and Ohio river valleys- man dogs and cats
Impaired CMI- will infect normal animals dependent on dose.
granulomas in lungs- a bit TB like
infection of macrophage- yeast cells gather together in macrophages (esp. alveolar macs)
Nitrogen within bird feces helps organism grow in soil. wind/dust helps aerosolize spores.

24

Histoplasma capsulatum farcinimosum

epizootic lympangitis
spores enter through skin
ulcers over lymphatics and LNs
in horses mostly
rare fungal pathogen
india, africa, middle ast

25

Zygomycetes

environmental fungi
broad hyphae, non-septate
asexual spores in a sporagnium
sexual spores oospores or zygospores
Mucor, Rhizopus, absidia, saprolengia
Infection uncommon in health animals
Immunodeficiency, steroids, ABX and diabetes
Abortion in cattle and rumentitis.
No cross walls- hyphae v. broad compared to other hyphael fungi.

Easy to identify because fungus basically follows you off the plate- rapid growth within 24 hours.

26

Mucor

Hyphae
grow fast in cultue
greyish-white aerial mycelium
pinhead fruiting heads full of spores
causes mycotic abortion, rumen ulcers, systemic mycosis in young or debilitated animals
Meat spoilage--> "whiskers" on bacon.

27

Antifungal chemotherapy

Cell wall inhibitors, cell membrane inhibitors
direct membrane damage (punch holes and lyse membranes), disruption of microtubules and inhibition of mitosis (for dermatophyte infection), nucleic acid synthesis inhibitors (can't use on it's own d/t rapid resistance); inhibition of protein synthesis.

Animal cell membranes have cholesterol, yeast/fungal membranes have ergosterol.

Selective toxicity: antifungals target bits that are unique to fungi and not common to mammalian/animal cells.

28

Mycotoxins

Secondary metabolites of fungal species in crops, pasture or stored feed. Low molecular weight, heat stable, non-antigenic, immunosuppressive, mutagenic, teratogenic, carcinogenic
Acute or chronic intoxication- Pencilium, Aspergillus, fusarium
Clinical dz: period of exposure, amount ingested

29

Aflatoxin- difurancoumarins

Aspergillus species- Aflatoxicosis: absorption from GI tract, metabolized by liver to toxic product--> carcinogenic.

30

Ergotism- ergopeptide alkaloids

claviceps purpurea- domestic animals and humans
seed heads of grasses and cereals. ergotamine and ergometrine--> affect nerves supplying arteriolar smooth muscles