MYCOLOGY Xiao-Kui Guo PhD Classification Based on molecular evidence: base sequences from ribosomal RNA (Patterson & Sogin 1992) Comparison of fungi and bacteria featurefungibacteria diameter4um1um nucleusEukaryoticprokaryotic cytoplasmMitochondria and endoplasmic reticulum present Cell membraneSterols presentSterols absent Cell wallchitinpeptidoglycan sporesSexual and asexual spores for reproduction Endospores for survival, not for reproduction Thermal dimorphism yesNo metabolismRequire organic carbon; no obligate anaerobes May do not require organic carbon; many obligate anaerobes Medically important fungi Includes 4 phyla Ascomycota - Sexual reproduction in a sack called an ascus with the production of ascopspores. Basidiomycota -Sexual reproduction in a sack called a basidium with the production of basidiospores. Zygomycota - sexual reproduction by gametes and asexual reproduction with the formation of zygospores. Mitosporic Fungi Fungi Imperfecti - no recognizable form of sexual reproduction. Includes most pathogenic fungi. Structure of fungi Morphology Unicellular fungi Multicellular fungi Hypha: mycelium (vegetative, aerial or reproductive). Spores: asexual spore a) Conidium : macroconidium, microconidium. b) Thallospore : blastospore , chlamydospore ,arthrospore . c) Sporangiospore( Multicellular fungi Hypha spore Hypha Dimorphism Culture Sabouraud culture medium optimal pH 4-6 optimal temperature C some deep pathogenic fungi need 37 C, Aerobic types of colonies yeast, filamentous Multiplication:budding, hypha formation, branching or disruption of hypha, spore formation Resistance Resistant to dry, sunlight, UV light and many chemicals Sensitive to wet heat four types of mycotic diseases: Hypersensitivity - an allergic reaction to molds and spores. Mycotoxicoses - poisoning of man and animals by feeds and food products contaminated by fungi which produce toxins from the grain substrate. Mycotoxin and tumor Mycetismus - the ingestion of toxin (mushroom poisoning). Infection Immunity Nonspecific immunity Specific immunity DIAGNOSIS 1. Skin scrapings suspected to contain dermatophytes or pus from a lesion can be mounted in KOH on a slide and examined directly under the microscope. 2. Skin testing (dermal hypersensitivity) used to be popular as a diagnostic tool. 3. Serology may be helpful when it is applied to a specific fungal disease. 4. Direct fluorescent microscopy. 5. Biopsy and histopathology. 6. Culture. Pathogenic fungi are usually grown on Sabouraud dextrose agar. It has a slightly acidic pH (~5.6); cyclohexamide, penicillin, streptomycin or other inhibitory antibiotics are often added to prevent bacterial contamination and overgrowth.