Mycology II

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Microbiology and Immunology
Microbiology and Immunology 2500A/B

Lecture 10: Mycology II 10/01/2012 Molds  Laboratories without biological safety cabinets must not work on any mold, except those believed to be dermatophytes  There are several identification criteria: 1. Growth rate in culture 2. Presence of a yeast phase (is it dimorphic?) 3. Colonial and microscopic morphology (most important) 4. Biochemical tests Mold Classification  Examination of the hyphae enables classification into 3 groups: 1. Septate unpigmented hyphae (hyaline). Includes the majority of medically important molds. 2. Septate brown pigmented hyphae (dematiaceous) 3. Aseptate wide hyphae, characteristic of the lower fungi Mucorales Hyaline Hyphae  Hyaline – means looks like glass  No pigment Hyaline Molds: Aspergillus  Smoky, gray/green fuzzy colonies  Invasive infections in severely immunocompromised patients, especially with prolonged neutropenia. Mortality is greater than 50%  Cause chronic sinusitis and aspergilloma (fungus ball in preexisting pulmonary cavity) in immunocompetent patients  Aspergillus species: 1. Aspergillus fumigatus also causes allergic bronchopulmonary aspergillosis in asthmatics and CF patients 2. Aspergillus niger commonly causes otomycosis 3. Aspergillus flavus may infect immunocompromised patients and also infects peanuts, producing aflatoxin which is associated with liver carcinoma 4. Aspergillus terreus Aspergillus Hyphae in Tissue  Tissue biopsy – need silver stain to differentiate fungal elements  Repeated branching, but eventually end up going in the same direction (same behaviour as schooling fish) Hyaline Molds: Penicillium  Rapidly growing greenish colony which you often see on moldy bread  Source of penicillin  One invasive species: Penicillium marneffei  Penicillin – inhibits bacterial growth Dermatophytes  Trichophyton spp. (red colony – makes it easy to identify)  Microsporium spp.  Epidermophyton floccosum Tinea Pedis (Athelete’s Foot)  Dark, moist conditions to get Athlete’s foot  Fungal infection of the foot Tinea Corporis (Ringworm)  When it happens on the body, it is called ringworm  Fungal infection of the body Chromoblastomycosis  Disfiguring infections due to demataceous fungi  Phialophora verrucosa, Fonsecaea compacta,  Fonsecaea pedrosoi most common Cladosporium carrionii, Rhinocladiella aquaspersa  Dx: Histology and culture: Medlar bodies  Not expected to know any of these names (“copper pennies”)  Rx: Excision and posaconazole Aseptate Hyphae: Order Mucorales  Common in soil and decaying vegetation  Infection called mucormycosis 1. Rhizopus 3. Mucor 2. Absidia 4. Cunninghamella Mucormycosis  More common in immunocompromised patients  Usually starts in nose or paranasal sinuses, especially in debilitated patients with nasogastric tubes  One of the most rapidly spreading fungal infections  Poor prognosis  Rhizopus Spp. – rhizoids directly below sporangiophore  Absidia Spp. – rhizoids not directly below sporangiophore  Mucor – no rhizoids Diagnosis of Mold Infections  Superficial: clinical  Deep: 1. Initial detection of hyphae in biopsy specimens 2. Culture 3. Aspergillus is a common lab contaminant: diagnosis is mainly via biopsy correlated with the clinical findings, X-ray and CT scan (halo sign on lung CT) Indoor Molds and “Sick Building Syndrome”  Only immunocompromised people are at risk for invasive infection with environmental molds  Atopic people (15%) may develop hypersensitivity reactions such as allergic rhinitis, asthma, and itchy eyes  Volatile organic compounds have musty s
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