intro to fungi

Page 1

What are fungi?

Moulds

Most common

Grow in damp, wet and badly aerated conditions

Mushrooms

Food industry

Yeasts

Microscopic

Food industry

Smuts

Found on maize

Truffles

Food industry

Terminology

Mykos - fungus/mold

Mycology - study of fungi

Mycosis - a disease caused by toxins produced by a fungus

Mycetism - poisoning from ingestion of toxic substances present in a mushroom

Ecology

Ubiquitous- widely distributed in nature

Can be saprophytic or pathogenic

Main roles

decomposers

symbionts

parasites

Only small fraction are dangerous to humans

Features

Different kingdom to animals and plants

Eukaryotic with highly developed cellular structure

Aerobes

Optimum graph at 20-30 degrees

Non-photosynthetic

Can be unicellular or multicellular

Non-motile

Produce spores

Sexual and a sexual reproduction

Resistant to antibacterial drugs

classifications

Yeast

Unicellular

Macro

pasty colonies resemble bacteria

Micro

Oval to round 3-5

Reproduce by budding

In the tissue

Pseudohyphae

Mould (Hyphae)

Multicellular

Top and bottom different colours and textures (allows identification)

Macro

Surface texture

Cottony

Wooly

Velvety

Granular

Pigmentation

Observed from the reverse

Micro

Hypha

Often bearing spores

Hyphae- masses of multicellular filaments

Mycelium - groups of hyphae

Hyphae grow at their tips, new tips form by branching

Hyphae can be classified into two groups

Septate - hyphae contain cross walls

Nonseptate - hyphae dont contain cross walls

Fungal cell walls made of chitin

Aerial hypha support spore bearing structures

NB there was something about ergosterol, azaleas and amphotericin B here, but I don't understand the notes and there is no stream capture as of yet.

Spores

Not as durable as bacterial endospores

Serve as reproductive mechanism

Useful identification

Asexual reproduction - spores develop into new organism using mitotic division

Sexual reproduction

Free spores - conidia

Spores formed within a sac - sporangiospores

New mycelium is formed

Dimorphic

Capable of growing in mould or yeast forms under different environmental conditions

yeast like 37 degrees

mould like 25 degrees

Different morphologies dependent on temp they are grown at

Sporothrix schenckii-cutaneous infection (skin infection) example in human and animals

Lab must take both temp cultures

Uses

Biodegradation

Absorb nutrients from environment

Woot rotting fungi

Decomposers . Break down organic materials and return components the earth

Industrial uses

Biochemicals

Production of soy source

Production of citric acid

Direct sources of food

Quorn mycoprotein

Cultivated mushrooms

Food industry

Bakers yeast to produce alcohol and bread

Create cheeses

Medicine

Penicillin

Cephalosporin

Griseofulvin

Statin - used to treat raised cholesterol

Cyclosporin A - inhibits rejection of transplanted organs

Fungal disease

Mechanisms

Tissue invasion- Mycosis

Superficial/Cutaneous (Dermatomycosis)

Hair

Skin

Nail

Cornea

Subcutaneous

Dermis and subcutaneous tissues

Systemic

Invades internal organs

Highly virulent fungi

Not found in UK and dimorphic

Blastomycosis

Histoplasmosis

Coccidiomycosis

Found in UK , not dimorphic

Cryptococcus neoformans

Toxin production- Mycotoxicosis

Induction hypersensitivity- Recurrent Airway Obstruction (RAO)

Clinical examples

Cutaneous mycosis

Caused by dermatophytes

Geophilic

Zoophilic, see powerpoint for examples

Anthropophilic

Affinity for keratin

E.g. ringworm

Opportunistic mycosis

generally occurs if right conditions also occur such as

Immune deficient back ground

Debilitated animals

Prolonged antibiotic treatment (reduces normal flora)

Immunosuppression

Exposure to spores

Persistent moisture on skin surface

E.g.Aspergillus spp

Yeast

Lipophilic - affinity for fat

Commensal on oily areas of skin and ears of healthy animals and humans

E.g. cryptococcus neoformans

Animal and people

Not zoonosis--from environment not direct transmission

Primarily remains in upper airways

Can spread via blood and or tissue

Problem in immunocompromised patients

mycotoxicosis

Metabolites of certain fungal species

Produceced when toxigenic species grow on crop, pasture or stored feed

Same food is then ingested

Toxic affects

Immunosuppressive

Carcinogenic

Teratogenesis

NB abscence of fungus doesn't rule out presence of toxin

Clinical signs vary due to amount of toxin ingested

Certain mycotoxins are most potent carcinogens in existence

Outbreaks usually seasonal. and sporadic

Antimicrobial medication is ineffective

Most common is aflatoxicosis

Most potent natural carcinogen

Linked to

Increased mortality in farm animals

Acute aflatoxicosis -results in death

Chronic aflatoxicosis - results in cancer and immune suppression

Organ targeted is liver

Hepatopathy

Hepatic lesions

Pigs sensitive

Ergotism

From ingestion of cereals infected with claviceps purpurea

Sclerotum

2 forms

Gangrenous - affects blood supply to extremities

Convulsive- affects CNS

Clinical findings

Gangrenous necrosis of extramities

Abortion

Suppression of lactation

Affected limbs swollen with a defined line separating normal tissue