Fungal pathogens Flashcards
what are saprophytic fungi useful for?
degrading and recycling organic matter e.g. lignin and cellulose
what do phytopathogens cause?
rusts, smuts, rots, blights, mildews, galls and wilts
what is mycology?
the study of fungi
what is medical mycology?
the study of fungi pathogenic for humans
what type of cell are yeasts?
unicellular fungi, usually oval or round
how do yeasts reproduce?
by budding
how do moulds grow?
as filaments or hyphae
what is a mycelium?
a mass of hyphae
what does it mean fungi are dimorphic?
they can grow as yeasts or hyphae
are fungi eukaryotic or prokaryotic?
eukaryotic
other characteristics of fungi?
- non-motile
- non-photosynthetic
- have rigid cell walls
what are the causative agents and mycosis of superficial mycosis?
Malassezia globosa - tinea versicolor
Candida albicans - candidosis
what are the causative agents and mycoses of cutaneous mycosis?
Trichophyton spp. (Dermatophytes) - Athletes foot, ringworm
what are the causative agents and mycosis of subcutaneous mycosis?
Sporothrix - sporotrichosis
what are the causative agents and mycosis of systemic mycosis (primary, endemic?
Histoplasma capsulatum - Histoplasmosis
what are the causative agents and mycoses of opportunistic mycosis?
Candida albicans - candidosis
Aspergillus fumigatus - aspergillosis
Cryoptococcus neoformans - cryptococcosis
what is Pityriasis versicolor?
a superficial infection caused by Malassezia species, usually M. globes (M. furfur)
how does yeast reproduce in pityriasis versicolor?
by hyphae
does dermal penetration occur in pityriasis versicolor?
no
risks factors of pityriasis versicolor?
endogenous or exogenous corticosteroids seen in normal individuals; climatic factors or sun exposure
pityriasis versicolor’s symptoms
asymptomatic or mildly pruritic with scaling; confluent macule on the trunk, upper arms, or neck - these may be hypo pigmented or hyper pigmented
what is the most prevalent in superficial candida infections?
oral and vaginal ‘thrush’ and denture stomatitis
how do you treat superficial candida infections?
anti fungal treatment and treat predisposed factors (e.g. diabetes) and remove gut reservoir
what are dermatophytes?
septate branching hyphae
what is sporothrix schenkii?
chronic cutaneous or lymphocutaneous disease
how does the person gets sporothrix schenkii?
fungal spores enter through abrasions
what are primary pathogens?
mould and yeast
when are mould and yeast pathogenic?
in the environment and in tissue
how are systemic infections geographically restricted?
mostly in the USA, Central and South America
species associated with disease in systemic infections?
Histoplasma capsulatum, Blastomyces dermatitis, Coccidioides immitis
what enhances the growth of histoplasma?
by bird or bat excreta
how do yeasts remain in the lungs in histoplasma capsulate?
yeasts remain viable (latent - sub clinical) in lungs for years
what are opportunistic fungal infections?
most serious fungal infections worldwide
are opportunistic fungal infections geographically restricted?
no
what causes opportunistic infections?
candida, aspergillus and crytococcus species
what to opportunistic infections infect?
hosts with impaired defences
recognised risk factors included in opportunistic infections
- malignant disease, AIDS, burns, major surgery
- organ or bone marrow transplants
- antibiotic therapy, immunosuppressive therapy
- indwelling catheters
how are systemic candida infections?
many are endogenous, and some (e.g. bloodstream) are exogenous
where are aspergiullus infections found?
in air and soil, but not part of normal flora of humans
what do A.fumigatus produce?
aerial hyphae bearing conidia (spores)
what destroys inhaled conidia?
macrophages
process of the activity of host defences against Aspergillus?
- inactive conidia are inhaled
- conidia lodge in lower respiratory tract
- conidia swell
- blocked by macrophages
- conidia germinate into hyphae
- blocked by neutrophils
- hyphae invade tissues
- blocked by neutrophils
- hyphae invade blood vessels and disseminate
what is cryptococcus neoformans?
yeasts with a thick polysaccharide capsule
what happens during the infection of c. neoformans?
the polysaccharide is solubilised
what is cryptococcal meningitis?
localised in brain and CNS
how do agents have to be for anti fungal chemotherapy?
must be selectively toxic (more difficult with eukaryotic micro-organisms)
what are Amphotericin B or fluconazole used to treat?
treating systemic infections
