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Mycology – Yeast. Student Lab Division of Medical Technology Carol Larson MSEd, MT(ASCP). Basic Characteristics. Unicellular Generally normal flora. Basic Characteristics. Asexual reproduction Blastoconidia Pseudohyphae Arthroconidia. Direct Examination. - PowerPoint PPT Presentation
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Direct Examination
• Observe for reproductive structures
• Gram stain– Gram positive
• India ink stain– Capsules
Colony Morphology
• Appearance– Similar to bacteria colony
• Texture– Glabrous– May be filamentous
• Pigmentation
• Confuse with Staphylococcus
Yeast ID Methods
• Cornmeal-Tween 80 agar– Procedure– Observe microscopically for
• Chlamydospores• Blastoconidia• Pseudohyphae• Arthrospores
Yeast ID Methods
• Niger Seed Agar (Birdseed agar)– Procedure– Observe for brown pigment caused by
phenol oxidase activity– Cryptococcus
neoformans
Yeast ID Methods
• Urease– Procedure– Positive:
• Cryptococcus sp. (rapid)• Trichosporon sp.• Rhodotorula sp.
– Negative:• Candida sp.• Geotrichum sp.
Yeast ID Methods
• Carbohydrate assimilation– Utilize carbohydrate as sole source of
carbon in the presence of oxygen– Positive = growth
• Carbohydrate fermentation– Utilize a carbohydrate anaerobically– Positive = gas
Candida species
• Normal flora
• Leading opportunistic fungal infection in man
• Candidiasis– Mucocutaneous– Cutaneous– Systemic
Factors predisposing to infection
• Immunocompromised
• Malignancy
• Prolonged antibiotic therapy
• Lupus, Diabetes
• Pregnancy and use of birth control pills
• Age
• Damaged skin barrier
Candida albicans
• #1 fungal isolate in laboratory
• Germ tube: positive
• CMT: clustered blastoconidia at septa of pseudohyphae, terminal chlamydospores
• CHO: sucrose positive
Candida stellatoidea
• Germ tube: positive
• CMT: clustered blastoconidia at septa of pseudohyphae, terminal chlamydospores
• CHO: sucrose negative
Candida tropicalis
• Germ tube: negative
• CMT: sparse single or short-chained blastoconidia anywhere along pseudohyphae, rare chlamydospores
• CHO: sucrose positive
Candida glabrata
• Causes UTI
• Germ tube: negative
• CMT: only blastoconidia, no pseudohyphae
• CHO: only glucose and trehalose positive
Candida krusei
• Germ tube: negative
• CMT: tree-like branching of abundant blastoconidia from the septa of elongated pseudohyphae (“cross-matchsticks” appearance)
Candida pseudotropicalis
• Germ tube: negative
• CMT: branched pseudohyphae with chains of elongated blastoconidia – logs in a stream arrangement of broken up blastoconidia positioned parallel to each other
Candida parapsilosis
• Germ tube: negative
• CMT: few single or small clustered blastoconidia at or between septa of thin curved pseudohyphae. Sometimes giant pseudohyphae may be observed
Cryptococcus neoformans
• Germ tube: negative
• CMT: large, round blastoconidia, no pseudohyphae
• Urease: positive (within 3 hours)
Geotrichum candidum
• Geotrichosis– Mimics Candida infections– Infection in debilitated people
• Considered a mold
• Germ tube: negative
• CMT: arthroconidia andtrue hyphae
• Urease: negative
Trichosporon beigelii
• Causes White Piedra
• Germ tube: negative
• CMT: arthroconidia, true hyphae, rare blastoconidia
• Urease: positive
Rhodotorula species
• Saprophytic yeast found in soil
• Rarely a pathogen
• Often encapsulated
• Urease: positive
• Colony pigmentation: reddish-orange
Malassezia furfur
• Causes Tinea Versicolor
• Septicemia in patients receiving intravenous lipid therapy
• KOH: clusters of thick-walled, round budding yeast and short, straight or angular mycelial fragments (spaghetti and meatball appearance)
• Lipophilic