Intro to Fungi Flashcards
structure of fungi
-chemo-organotrophic eukaryote that lacks chlorophyll and forms spores
-its cell wall contains polysaccharides, often chitin or glucan, and it absorbs nutrients
-its membrane contains ergosterol as the major sterol
Classification of fungi
Based on morphology
Refer to major types as moulds, yeasts or mushrooms
3 fungal groups
Basidiomycets (mushrooms), ascomycetes, zygomycetes (moulds)
How do we officialy classify fungi
by their sexual spores produced
common diseases caused by fungi
- athlete’s foot: caused by Epidermophyton, Microsporum and Trichophyton spp
- thrush: caused by Candida spp
- pityriasis versicolor: caused by Malassezia spp
main dermatophyte virulence factor of fungi
enzyme(s) that degrade and utilize keratin as a nutrient source
dermatophytosis
- fungal infection of the skin
- causative agents= epidermophyton, microsporum and trichophyton
- moulds with a predilection to degrade keratin as a nutrient source
- dermatophytes can cause superficial infections of the skin, hair, and nails
- “ringworm” infections, usually called tinea
host factors contributing to pathogenicity of fungal infections
- Favourable micro-environments (warm, moist areas) encourage growth of fungi on skin and mucous membranes
- broad-spectrum antibacterial agents reduce competition for epithelial colonization sites in the gut
- immunosuppression of all types may create a window of opportunity for fungal invasion
Ways immunosupression of host defences can be caused
2 ways
*Iatrogenic= steroids, anti-cancer chemotherapy, solid-organ transplantation
*Disease processes=AIDS, leukaemia, endocrinopathies
*Combinations of both
Systemic fungal infections
- affect internal organs and are less common
- can be fatal in immunosuppressed patients
- treated with oral or parenteral agents
candida infections
-Candida spp. are yeasts
-clinical diseases= superficial (mouth, vagina, penis, skin, nails), deep-seated (disseminated infections in seriously immunocompromised hosts- neutropenia, abdominal surgery, major burns, etc.)
e.g. c.albicans
Explain the dissemination of candida spp
- Break in wall (e.g. GI tract due to venous catheter)
- Fungal particles (yeast) can escape into bloodstream (translocation) and become resistant to antifungal treatment
Chronic mucocutaneous Candida infection
can arise in individuals with an unusual combination of endocrine and immune dysfunction (autoimmune polyendocrinopathy-candidiasis-ectodermal dystrophy — APECED)
Aspergillosis
- causative species= aspergillus fumigatus, aspergillus flavus, aspergillus nidulans (in CGD patients), aspergillus lentulus, other species on rare occasions
- types of disease= simple asthma, asthma with eosinophilia, aspergilloma, invasive bronchopulmonary aspergillosis, disseminated aspergillosis
- route of infection= inhalation of conidia (spores through lungs)
invasive pulmonary aspergillosis
- mainly associated with haematological malignancy
- specific diagnosis very difficult
Cryptococcosis
can cause meniggitis (particularly in AIDS patients) and disseminated infection in severly compromised hosts
Damage-response interaction
Dont want too weak or strong of an immune resposne as both can be potentially harmful
diagnostic methods
- direct detection- histopathology, high-res CT scans
- dermatophytes visualised directly in skin scales
- direct smear= periodic acid shiff (PAS) -staining
detection of circulating fungal antigens
detection of circulating antibodies to fungi
PCR for fungal DNA
culture of fungus from normally sterile site
MALDI-ToF Biotyping
antifungal agents
- polyenes= e.g. amphotericin B (topical, IV, lozenge, ointment, oral suspension), nystatin (topical, pastille, oral suspension)
- azoles= e.g. clotrimazole, miconazole, several others (topical), fluconazole, itraconazole, voriconazole (oral and/or IV), posaconazole (oral)
- echinocandins= e.g. anidulafungin, caspofungin, micafungin (IV)
4 main antifungals and each of their functions
- Triaxoles/allylamines - target sterols
- Echinocandins p target wall
- Polyenes - target membrane
- Flucytosine - target DNA synthesis
problems with antifungals
*Spectrum of activity
*Static or cidal
*IV vs oral
*Toxicity
*Resistance
*Cost
