Flashcards in Intro to mycology Deck (21):
What is a fungus? Categories?
Eukaryotic kingdom. Few that cause disease. Larger than bacteria. Heterotroph, require preformed organic carbon. Mushrooms, yeast, mould
Chitin: Cell wall polysaccharide (mannan and glucan too), Distinguishes fungi from plant cells (cellulose), Adsorbs certain dyes, key identification feature; No cell wall in mammalian cells; Peptidoglycan is polymer in bacterial cell wall. Ergosterol: Cell membrane sterol (rigidity, Distinguishes fungi from mammalian cells (cholesterol) – Antifungal target
Unicellular, round/ovoid, asexual budding. Yeast are normal GI flora. Genus of note is candida, cryptococcus, malassezia. Microscopy look different, look for structure. Plated cultures hard to tell apart from bac.
Filamentous fungi, multicellular, filamentous, branching growth. Hyphae/mecelia, growth at the hyphal tip -reproduce primarily by conidia: asweual spores, give mould its colour, easily airborne (transmit, allergy, etc). Humans have no endogenous mould. Microscopy look like dandelion. Plates look fuzzy.
Superficial fungal diseases
aka cutaneous. The Dermatophytes have tropism for keratinized tissue – skin, hair, and nails; rarely invade deeper tissues. Athletes foot, ringworm
Subcutaneous fungal diseases
Deep, ulcerated skin lesions. Nodules pop up. Rarely invade deeper tissues. Sporotrichosis (Sporothrix). Not many of these.
Opportunistic fungal diseases
Not ‘true pathogens’, low virulence potential, Require immune compromise. ex. Aspergillus, Candida, Mucor, Cryptococcus
Endemic fungal diseases
aka. Systemic/Dimorphic. ‘True pathogens’, cause severe disease in healthy people. Restricted geographically. Usually involve lungs, as well as deep organs via dissemination. ex. Histoplasma, Blastomyces, Coccidioides
Limited. Most like 25-30C and slightly acidic pH. Innate immunity prevents most growth unless you have deficiencies etc.
Transmission methods of fungi
Inhalation — spores, conidia; Aspergillus, Endemic mycoses. Mucosal colonization – Candida. Skin break or injury – Candida, Sporothrix
Immune regonition of fungi
Opsonins (comp, AB), PRR, TLR bind fungi. Activate phagocytosis, cytokines, resulting in ingestion or extracellular phagocyte killing
Risk factors for invasive mycoses
Immunosuppression (Chemotherapy). Promotion of fungal colonization – Antimicrobial therapy. Direct access to blood, lungs, deep tissues – catheters, chemotherapy, Solid organ transplantation, Travel
Patients at high risk for invasive fungal infection (IFI)
HSCT (blood stem cell recipient) - depends on how bad; SOT (solid organ transplant) - may depend on type of organ
Diagnosing fungal disease
Specimen quality is very important. bronchial washing. Tissue or aspirate in sterile container. Not a lesion swab, sputum, stool (too much else going on). Microscopy (gram, silver) tells whether mould or yeast. Culture (yeast is smooth, round; and mould is fuzzy, filaments). Serology
Pros of microscopy
Quick (same day), see unique cell features, some are quickly identified
Pros and cons of culturing fungi
Confirms ID, usually unique features. Culture isn’t always positive, and it is slower (several days)
Antigen detection for fungi
Some assays for antigens, but fairly limited.
Serology for fungi
Look for AB, but usually there aren’t many. They general dono’t generate humoral response.
Polyenes, azoles (targets cell membrane) , enchinocandins (targets cell wall), nucleoside analog
Antifungal susceptibility testing
Test with broth microdilution (look at MIC); and disk diffusion (zone of inhibition). Determines if that anti fungal will be good or if they have resistance.