Introduction to Mycology PDF

Mycology ========  Mycology is the study of fungi - Taxonomy - Environmental impact - Genetic and biochemical properties Medical Mycology ================ - study of fungi and their relationship to human disease - encompasses - Single-celled yeasts  Filamentous molds - t...

Mycology ========  Mycology is the study of fungi - Taxonomy - Environmental impact - Genetic and biochemical properties Medical Mycology ================ - study of fungi and their relationship to human disease - encompasses - Single-celled yeasts  Filamentous molds - true pathogens -- historically pathogenic fungi  opportunistic pathogens -- saprophytic fungi - Immunocompromised host - Immunosuppressive infection: HIV/AIDS - High-dose cancer chemotherapy - Solid organ transplantation Overview of Fungi ================= - Diverse group of organisms - Classified as molds (filamentous) and yeasts (moist) - Categories - Classic pathogens - Environmental saprobes - May cause a range of signs and symptoms - Mild to life-threatening - Significant in the immunocompromised patient General Characteristics ======================= - Eukaryotic - Most fungi are saprophytic (they live on dead organic matter) - Fungi are yeasts (moist) and/or molds - Organisms that display both yeast and mold forms are dimorphic - They are thermally dimorphic when dependent on temperature General Characteristics (cont.) =============================== - Fungi that have more than one form or stage are polymorphic - Thick cell walls - Made of chitin - These properties allow the absorbing of specialized dyes used in identification (ID). - Mostly obligate aerobes - Prefer neutral pH Shared Characteristics ====================== - Chitin in the cell wall - Ergosterol in the cell membrane - Reproduction by means of spores sexually or asexually - Lack of chlorophyll - Lack of susceptibility to antibacterial agents Epidemiology ============ - Increased fungal infections worldwide - Immunocompromised patients - Use of antifungal medications - More than 135,000 valid species of fungi - 1000-1500 newly identified annually - Implementation of molecular technology will continue to impact the evolution of the field of mycology Yeasts ====== - Single vegetative cells - ID is primarily based on biochemical testing and molecular diagnostic methods. - Reproduction via budding or fission Formation of Blastoconidia in Yeast =================================== Molds ===== - Filamentous mycelium - Long strands of tubelike structures called *hyphae* - Reproduction by spores asexually or sexually - Vegetative mycelium - Arthrospores, chlamydospores, blastospores - Rhizoids - Aerial mycelium - Conidia, sporangia Visual Representation of Aerial and Vegetative Mycelia ------------------------------------------------------ Mold Morphology =============== - Shape - Antler - Racquet - Spiral - Rhizoids - Septate - Frequent perpendicular cross-walls - Sparsely septate - Frequent perpendicular cross-walls Septate Versus Sparsely Septate =============================== Hyaline Versus Phaeoid ====================== - Hyaline - Nonpigmented - Lightly pigmented - Phaeoid - Darkly pigmented Dimorphism and Polymorphism =========================== - Dimorphism - Ability to exist in two forms based on growth conditions - Mold phase - 22 to 25° C (room temperature) - Yeast phase - 37° C with increased carbon dioxide (CO~2~) - Polymorphism - The ability to form yeast and mold in same culture - Generally yeast first moving to mold as culture ages  Ex. *Exophiala* spp. Reproduction ============  Asexual reproduction - Conidia (conidium) following mitosis - Fruiting structures - Phialoconidia - Annellide ring structures - Phialides - Vase-like structures that produce phialoconidia - Annellides - Ringed structures that produce annelloconidia Asexual Reproduction Producing Phialoconidia -------------------------------------------- Formation of Arthroconidia ========================== Reproduction ============ - Sexual reproduction - Teleomorph - Anamorph - Occasionally reproduce asexually - Synanamorphs - Name for amorphic strains when more than one anamorph is present for the same teleomorph - Different asexual forms in the same fungus Zygospore Formation =================== Taxonomy Nomenclature =====================  Historically, fungi have carried multiple names (genera and species) associated with reproductive forms - Obsolete: The International Botanical Congress (July 2011) adopted a "one fungus, one name policy" published in the International Code of Nomenclature, Article 59. - International Code of Nomenclature for Algae, Fungi, and Plants (January 1, 2013) Taxonomy of Clinically Significant Fungi ----------------------------------------  The causative agents of clinical infections are found in four groups of fungi - Asexual reproduction by conidia - Sexual reproduction by ascospores  Phylum Basidiomycota - Sexual reproduction via basidiospores (on basidia) Taxonomy of Clinically Significant Fungi ----------------------------------------  The causative agents of clinical infections are found in four groups of fungi - replaced Phylum *Zygomycota* - Asexual reproduction by sporangiospores - Sexual reproduction by zygospores  Fungi Imperfecti - formerly classified in the form phylum *Deuteromycota* no sexual phase Mucorales ========= - Rapid growers - Produce gray to white aerial mycelium with hyaline, sparsely septate hyphae - Opportunistic pathogen in the immunocompromised  Asexual reproduction - Sporangiophores and sporangiospores - Results in zygospores (not seen in clinical laboratories) - Example members---*Mucor, Rhizopus, Lichtheimia* Asexual Reproduction by Mucorales --------------------------------- Ascomycota ========== - Sexual spores - Ascospores Contained in a saclike structure - Species - *Microsporum* spp. - *Trichophyton* spp. - *Scedosporium boydii* Basidiomycota ============= - Only pathogen - *Filobasidiella neoformans* Sexual form of *Cryptococcus neoformans* var. *neoformans* - Other genera associated with human infections - *Malassezia, Trichosporon* - ID - Clamp connections at septations Fungi Imperfecti ================ - Contains the largest number of causative agents of mycoses - Organisms are placed in this group when no mode of sexual reproduction has been identified. - These organisms are identified on the basis of characteristic asexual reproductive structures. - Examples: *Ulocladium, Alternaria tenuis* Parafungal Organisms ==================== - Organisms that resemble yeast and Protozoans - Remain unculturable - Atypical agents of human infections