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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.
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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 • Observe for reproductive structures • Gram stain • Gram positive • India ink stain • Capsules
Growth Requirements • Growth in 2-3 days • Temperature • 25-37ºC • Best at 30ºC
Colony Morphology • Appearance • Similar to bacteria colony • Texture • Glabrous • May be filamentous • Pigmentation • Confuse with Staphylococcus
Yeast ID Methods • Germ Tube Production • First test performed when yeast • Procedure • Interpretation
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
Yeast ID Methods • Commercial identification kits • Manual methods • Automated methods
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 • Cryptococcosis • Pulmonary • Meningitis • Pigeon droppings
Cryptococcus neoformans • Gram stain • India ink stain
Cryptococcus neoformans • Germ tube: negative • CMT: large, round blastoconidia, no pseudohyphae • Urease: positive (within 3 hours)
Cryptococcus neoformans • Niger seed agar: brown pigment
Cryptococcus neoformans • Cryptococcal antigen test
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
Saccharomyces species • Rarely a pathogen • Ascospores (acid fast positive)
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
In Summary … • Key characteristics of yeast • Identification methods • Germ tube • CMT • Biochemical tests • Clinically significant yeast • Candida albicans • Cryptococcus neoformans