Mycology

Year 1 - Semester 1

which is the largest fungal phylum?

ascomycota

general features of fungi

eukaryotic, highly developed cellular structure, aerobes, some strict aerobes with optimum temp of 20-30 degrees, non-photosynthetic (lack chlorophyll), absorb nutrients from their environment, resistant to antibacterial drugs, unicellular or multicellular, rigid cell walls make them non-motile, reproduce sexually or asexually via spores

3 main morphological forms of of fungi

yeast, mould and dimorphic

dimorphic fungi

fungi that is both yeast- and mould-like

macroscopic appearance of fungal yeast

pasty colonies that resemble bacteria

microscopic appearance of fungal yeast

large oval/round cells that reproduce by budding

macroscopic appearance of fungal mould

cottony/velvety/granular texture with a range of pigments

microscopic appearance of fungal mould

branching, thread-like filaments called hyphae form a tangled mass called mycelium

hyphae

multicellular filaments of fungi which form myceliums together, they grow radially at the tips of fungi and form branches

2 types of fungal spores

sexual and asexual

function of fungal spores

to allow asexual and sexual reproduction to occur

main components of fungal plasma membranes

chitin and ergosterol

examples of anti-fungal agents

polyenes, azoles, allylamines, echinocandins, griseofulvin

how do polyenes work?

they bind to ergosterol and disrupt fungal cell membranes

how do azoles work?

they interrupt enzymatic synthesis of ergosterol

how do allylamines work?

they inhibit fungal squalene which is a key precursor to ergosterol

how do echinocandins work?

they disrupt fungal cell glucan synthesis which causes cell lysis

how does griseofulvin work?

it inhibits mitosis of fungal cells

positive effects of fungal metabolites

plant growth regulators, pigments/dyes, used in cheese making, microbial enzymes, anticancer, health benefits, antibiotics

negative effects of fungal metabolites

plant diseases, mycotoxins, food spoilers

main mechanisms for the spread of fungal diseases

tissue invasion, toxin production, induction of hypersensitivity

dermatophytes

fungal organisms that require keratin for growth so embed in keratinised layers of the skin, nails or hair, causing superficial mycosis which classically presents as ring worm lesions

histological appearance of microsporum dermatophytes

boat shaped macroconidia, no microconidia

histological appearance of trichophyton dermatophytes

lots of microconidia, cigar-shaped macroconidia

mycotoxins

metabolites of certain fungal species which are produced when toxigenic species grow on crop, pasture or stored feed

mycotoxicosis

ingestion of food contaminated with mycotoxins

2 main types of asexual fungi spores

sporangiospores and conidia

importance of fungal spores

allows identification of fungi, able to reestablish an entire mycelium, spread fungi in the environment

uses of fungi

biodegradation, industrial fermentation processes, source of protein-rich food products, bioremediation, symbiotic relationships with plants used in agriculture, biological control of pests, production of antibiotics

3 main types of mycotic/fungal disease

true mycosis, mycotoxicoses, hypersensitivity

true mycosis

when fungi invade tissue causing a host response

mycotoxicoses

when animals are poisoned by food products contaminated by fungi which produce toxins

fungal hypersensitivity

an allergic reaction to fungal moulds and spores

where does superficial/cutaneous mycosis occur?

hair, skin or nails

where does subcutaneous mycosis occur?

dermis or subcutis

where does systemic mycosis occur?

internal organs

types of dermatophytes

geophilic (soil associated), zoophilic (animal associated), anthropophilic (human associated)

factors that make patients more susceptible to fungal infections

prolonged antibiotic therapy, underlying disease, breakdown of mucocutaneous barrier (usually through trauma), immunosuppression, exposure to heavy load of fungal spores

opportunistic mycosis

fungal infection which occurs almost exclusively in patients whose normal defence mechanisms are impaired, caused by fungi which have a very low inherent virulence

main effects of mycotoxins

immunosuppression, developmental defects caused by exposure during pregnancy, carcinogenesis, accumulation in tissues of food producing animals causes human exposure

aflatoxicosis

poisoning from aflatoxins produced by Aspergillus fungi, toxins mainly target the liver

ergotism

a poisoning from ergot fungus that can cause gangrenous or convulsive symptoms due to contaminated grains like rye