Yeast Flashcards
Yeast General Info
Normal flora of the oropharynx, GI tract, and urogenital tract
Unless predominant numbers are clinical insignificant
Candida albicans Colony Morphology
Cream colored, pasty, smooth colony
May form spider-like or starry-feet projections with age
Candida albicans Microscopic
After 3 days - pseudohyphae with clusters or round blastoconidia form at the septa and large, thick walled, terminal chlamydospores develop
37 C - inhibits chlamydospores
Candida albicans Pathogenicity
1) Mucocutaneous Candidiasis - oral cavity (thrush), vaginal canal, trachea, and bronchi
2) Cutaneous Candidiasis - infection of skin and involves moist areas like fingers, toes, armpits, etc
3) Systemic Candidiasis - rare condition of debilitating, neoplastic, or immunosuppressive diseases
Candida albicans Germ Tube
Positive
C. albicans var stellatoidea may also give a positive
Candida tropicalis Colony Morphology
Creamy with mycelial fringe (looks like fungus on edges)
Candida tropicalis Microscopic
After 3 days - blastoconidia singly or in pairs of very small groups along pseudohyphae. A few teardrop shaped chlamydospores.
“Mickey Mouse Ears”
Candida tropicalis Pathogenicity
Cause infections in patients with:
1) Breakdown of body’s immune system
2) Prolonged treatment with antibiotics, corticosteroids, or cytotoxic drugs
3) Diabetes mellitus
4) Drug addicts
5) Found without evidence of disease
Candida tropicalis Germ tube
Negative
Candida parapsilosis Colony Morphology
Creamy, sometimes develops a lacy appearance
Candida parapsilosis Microscopic
After 3 days - round to oval blastoconidia formed singly or in small clusters are seen along the pseudohyphae
Large hyphal elements called giant cells may be present
Candida parapsilosis Pathogenicity
Considered nonpathogenic
Has been known to cause infection in susceptible individuals
Candida parapsilosis Germ tube
Negative
Candida kefyr Colony Morphology
Creamy and smooth
Candida kefyr Microscopic
3 days - forms pseudohyphae with found to elongate blastoconidia that can become detached from pseudohyphae
“logs in a stream”
Candida kefyr Pathogenicity
Usually nonpathogenic
May cause infection in susceptible individuals
Candida kefyr Germ tube
Negative
Candida krusei Colony Morphology
Flat, dry, dull
Developing a mycelial fringe
Candida krusei Microscopic
3 days - form pseudohyphae with elongate blastoconidia creating a cross-match sticks or treelike appearance
Candida krusei Pathogenicity
Nonpathogenic
May cause infections in susceptible individuals
Candida krusei Germ tube
Negative
Candida krusei Urease test
Positive
Candida guilliermondi Colony Morphology
Flat, glossy, smooth, edged, cream color, may develop slight pink color with age
Candida guilliermondi Microscopic
3 days - forms small yeast cells and relatively few short pseudohyphae often having small clusters of blastoconidia at septa
Candida guilliermondi Pathogenicity
Nonpathogenic
May cause infection in susceptible individuals
Candida dubliniensis Colony Morphology
Cream colored, pasty, smooth
Candida dubliniensis Microscopic
Chlamydoconidia are often attached at end of short, hyperbranching pseudohyphae and in a characteristic triplet or pair arrangement
Candida dubliniensis Pathogenicity
Primarily associated with HIV patients
Concern that this is more virulent than C. albicans - developing fluconazole resistance
Candida dubliniensis Germ tube
May be positive
Candida dubliniensis Chromagar
Colonies are green but lighter than C. albicans
Candida auris General Info
Emerging pathogen originally isolated in Asia
Antifungal resistance is common
Easily transmissible from person to person
Candida auris first isolation
Ear canal of patient in Japan
Trichosporon species
Two of interest:
1) T. beiglii
2) T. capitatum
Trichosporon Colony Morphology
Yeastlike
At first cream colored, moist, soft
Later finely wrinkled, heaped, and darkens to yellowish-grey
Trichosporon species Microscopic
3 days - true hyphae and pseudohyphae with blastoconidia singly or in short chains.
Arthroconidia form on older cultures
Trichosporon species Pathogenicity
T. beiglii causes white piedra
Occurs almost exclusively in immunocompromised patients
Trichosporon species Germ tube
Negative
Trichosporon species Urease test
Positive
Geotrichum candidum Colony Morphology
Young colonies: white, yeast-like
Mature colonies: Submerged hypae at periphery giving ground glass appearance
Most strains do NOT grow at 37 C
Geotrichum candidum Microscopic
3 days - true hyphae form that segment into rectangular arthroconidia, varying in size
NO blastoconidia along hyphae
NO alternating of light/dark
Geotrichum candidum Pathogenicity
Causes geotrichosis - rare infection that may produce lesions in the mouth, intestines, and lungs
Cause disease mostly in immunocompromised hosts
Cryptococcus neoformans General Info
Widely distributed in soil mixed with excreta from poultry
Common infection in AIDS population
Cryptococcus neoformans Colony Morphology
Begins as smooth white to tan colony, may become mucoid
Cream to brown with age
“Stringy” when trying to remove colony
Cryptococcus neoformans Microscopic
No pseudohyphae,
Irregular sized, spherical, thick-walled yeast cells with spaces between them
Cryptococcus neoformans Urease
Positive
Cryptococcus neoformans Nitrate
Positive
Cryptococcus neoformans India Ink
Positive for capsule
Cryptococcus neoformans Niger Seed Agar
Positive
Detects phenol oxidase production of yeast resulting in production of melanin
Red-brown pigment
Cryptococcus neoformans Pathogenicity
Cryptococcosis
Subacute or chronic infection most frequently involving CNS (meningitis)
AIDS patients
Cryptococcus albidus General Info
Common transient on human skin and has been reported as rare cause of pulmonary, CNS, and vaginal infections
Cryptococcus albidus Colony Morphology
Cream colored
Smooth to mucoid
Yeast-like
Cryptococcus albidus Microscope
SAB - demonstrates globose to avoid budding yeast-like cells or blastoconidia
Cryptococcus albidus India Ink
Positive
Cryptococcus albidus Urease
Positive
Cryptococcus laurentii General Info
Rare cause of pulmonary and cutaneous infection and continuous ambulatory peritoneal dialysis (CAPD)
Cryptococcus laurentii Colony Morphology
Cream colored, sometimes a deeper orange-yellow with age
Smooth mucoid texture
Cryptococcus laurentii Microscopic
SAB - produces spherical and elongated budding yeast-like cells or blastoconidia
Cryptococcys laurentii India Ink
Positive
Cryptococcus laurentii Urease
Positive
Candida glabrata Colony Morphology
Small yeast-like colonies
Pasty, smooth
White to cream
Candida glabrata Microscopic
CM 3 days - demonstrates only small, round to oval, single terminal budding
Nonencapsulated yeast cells, tend to form compact clusters
No pseudohyphae
Candida glabrata
Assimilates only glucose and trehalose
Candida glabrata Pathogenicity
Causes torulopsosis
Infection occurring usually in blood stream or UTI, sometimes in the lungs
Rhodotorula species Colony Morphology
Pink to coral
Yeast-like
Soft and smooth
Rhodotorula species Microscopic
CM 3 days - demonstrates budding round or oval cells variable in size with rare rudimentary pseudohyphae
No ascospores
Rhodotorula species Urease
Positive
Rhodotorula species Pathogenicity
Associated with contaminated equipment such as catheters, contaminated IV solutions and brochioscopes
Infections are present in terminal stages of debilitating disease
Saccharomyces species Colony Morphology
Smooth, moist
White to cream colored
Saccharomyces species Microscopic
CM 3 days - demonstrates yeast cells of various shapes with multilateral budding
Few very short pseudohyphae
Saccharomyces species Kinyoun stain
Characteristic ascospores seen when stained with Kinyoun and grown on special media
Saccharomyces species Pathogenicity
Usually nonpathogenic
Has been implicated in various infections in predisposed individuals
Prototheca wicherhamii Colony Morphology
Soft, wet yeastlike
White to light tan colonies
Prototheca wicherhamii Microscopic
Large non-budding cells with a symmetrical morula-like structure
Organism resembles algae Chlorella
Prototheca wicherhamii Pathogenicity
Previously thought to be a skin saprophyte
Now identified as rare opportunistic pathogen
Malssezia furfur General Info
Cause of tinea versicolor
Characterized by superficial scaly areas
Lesions occur on smooth surfaces of body
Causes disseminated infection in infants and young children
Malassezia furfur Colony Morphology
Organism will grow in yeast form only when media has been overlaid with 1-2 ml of olive oil
Malassezia furfur Microscopic
CM 3 days - no pseudohyphae or true hyphae formed
Round to oval cells
Conidia are produced on a broad base (shoulders may be seen)
Germ Tube Positive Organisms
Candida ablicans
Candida dubliensis - some strains, not all
Trichosporon species
Hyphae present
Arthroconidia positive
Urease positive
Candida species
Hyphae present
Blastoconidia positive
Cryptococcus species
Hyphae not present
Urease positive
Inositol assimilation
Nitrate positive
Rhodotorula species
Hyphae not present
Urease positive
Inositol negative
Candida glabrata
Hyphae not present
Urease negative
Small cells on Cornmeal
Dextrose positive
Trehalose positive
