Transcript Micrococcaceae

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
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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
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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 albicans
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 (“crossmatchsticks” 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 and
true hyphae
• Urease: negative
Trichosporon beigelii
• Causes White Piedra
• Germ tube: negative
• CMT: arthroconidia, true hyphae, rare
blastoconidia
• Urease: positive
Rhodotorula species
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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