Fungi Flashcards
What is a fungi?
- Chemo-organotrophic eukaryote
- Lack chlorophyll, means it doesn’t synthesise
- Produce spores
- Cell wall absorbs nutrients, also contains polysaccharides
- Membrane contains ergosterol
Chemotroph
Bond energy is released from a chemical compound
Organotroph
Organic compounds are used as electron donor
Structure of fungi
- Spores
- Hypha
- Clamp connection
- Septa
Spores
- Conidiospore with chains of conidia are where the spores are being dispersed of
- Produced when conditions are less than ideal, conidiophores can form and release spores into the environment
Hypha
- Branch out, filamentous structure
- One or more cells surrounded by tubular cell wall
3 groups in fungal kingdom
- Basidiomycetes
- Ascomycetes
- Zygomycetes
All can cause human disease
Basidiomycetes
E.g. Cryptococcus species Sexual spores: basidiospores Asexual spore: conidium Examples: mushrooms Releases basidospores
Ascomycetes
E.g. Candida, aspergillus spp. Sexual spore: ascospore Asexual spore: conidium Examples: Neurospora, saccharomyces Contained within sac
Zygomycetes
E.g. rhizopus spp.
Sexual spore: zygospore
Asexual spore: sporangiospore
Examples: Bread moulds
Yeasts
Fungi that favour a unicellular habit
Mother cells form bud and when bud becomes same size as mother cell it can split off
e.g. Candida spp. are yeasts
Athlete’s foot
- Epidermophyton, microsporum and Trichophyton spp.
Thrush
Candida spp.
Pityriasis vericolor
Malasszia spp.
Also form hyphae in infected skin
Tinea
Ringworm
Caused by dermatophytes: epidemophyton, microsporum and trichophyston spp. Moulds with a predilection to degrade keratin as a nutrient source
Face - facei, barbae - beardy area, coporis - tummy, cruris - pubic area, manum - hand, pedis - feet, unguium - toenails
How can fungi be fatal?
Act as an opportunistic pathogen of immunocompromised patients
Candida spp. as a fatal disease
- Infect deep organs of patients with various types of immune dysfunction e.g. after abdo surgery, burns etc.
- Can exist in mucosal membranes and can enter blood after surgery and nd up in non-mucosal organs
Aspergillus spp. as a fatal disease
- Infect deep organs of patients undergoing chemotherapy, stem cell transplantation
Pathgenecity of fungal infections
- Favourable micro-environments (warm, moist areas) encourage growth of fungi
- Broad-spectrum antibacterial agents reduce competition for epithelial colonisation sites in gut
- Immunosuppresion
Immunosuppression of host defences examples:
Iatrogenic: steroids, chemotherapy, solid-organ transplantation
Disease processes: AIDs, leukaemia, endocrinopathies
Candida examples
Albicans - Oral Tropicalis - Vaginal Glabrate - Skin Krusei - Nail Parapsilosis - Oesophageal Other spp. - UTI and disseminated infections (seriously immunocompromised)
Aspergillosis examples
Fumigatus - simple asthma
Flavus - asthma with eosinophilia
Other spp. - Aspergilloma, aspergillosis
Aspergillosis
- Moulds found in the environment, inhaling conidia all the time
- Strongly angioinvasive, penetrate walls of blood vessels
- If immunosuppressed can infect body, hyphae can grow and inseminate blood vessels
- Very difficult to treat due to membrane-type surround
Cryptococcus examples
Neoformans - pulmonary cryptococcosis
Gattii - yeasts with a capsule, meningitis as can cross BBB. Disseminated infection for immunocompromised
Diagnostic methods
- Direct detection: histopathology, high-res CT scan
- Growth on selected medium: chlorogenic substrate can break down and show different colours for different strains
- Detection of circulating fungal antigens
- Detection of circulating antibodies to fungi
- PCR for fungal DNA
- Culture of fungus from normally sterile site
Histopathology
- Biopsy, can stain the hyphae
- Dermatophytes visualised directly in skin scales
- Direct smear
High-res CT scans
- Hepatic Candida infection
- Aspergillosis, can see typical halo around it
Factors to consider in fungal treatment
- Spectrum of activity
- Static or cidal
- IV or oral
- Toxicity
- Resistance
- Cost
