fungi as pathogens

true pathogens

affect healthy host - usually asymptomatic, adapted to high temp and low O2 tension, restricted to specific regions, not obligate parasites

thermal dimorphism

change in temp cues a change in form of yeast

true pathogen natural habitat form

hyphal form, <30C, reproduction by spores, saprophytic

true pathogen animal habitat form

yeast form, 35-40C, reproduction by budding or endospores (cell forms and spores form inside), parasitic

opportunistic pathogens

immunocompromised host, worldwide, many species and genera, no specific adaptations to host environment but hardy to it

dermatophytes

superficial infections on healthy host, non invasive, don't cause disease, worldwide, most common cause ringworm and athletes foot

control of fungal diseases in humans

azoles, polyenes, 5-fluorocytosine

ergosterol

cholesterol equivalent

azoles function

interrupts an enzyme to block demethylisation of ergosterol, keeps membrane fluid so it can't function properly

polyenes function

inserts into membranes and makes a pore so cytosol leaks out and kills cell, high affinity for ergosterol so doesn't affect host membranes

5-fluorocytosine

inhibits RNA synthesis, fungus takes it up more than host so it accumulates in fungi

phytopathogenic fungi

plant pathogens

pathogens of immature/compromised tissue

broad host range, soil borne pathogens attack roots, aggressive invasion of root tips, water logged soils

necrotrophic pathogens

excrete toxins and cell wall digesting enzymes, induce host cell death, tissue invasion, evoke host resistance mechanisms, eg. armillaria mellea

biotrophic pathogen

maintain host viability, doesn't kill plant, limited tissue invasion, life cycle depends on host

haustorial biotrophs

spores infect cell, form haustorium - only breaks into cell wall, takes up nutrients from plant so reduces crop yield