mycology - true yeasts

yeast and yeast like organisms

refers to unicellular organisms that generally reproduce by budding

pseudohyphae

if the buds elongate and remain attached to the parental cell, this is _____

glabrous

colonies are _____ and can range from moist to dry

yeast

most common fungi isolated in the clinical laboratory

cornmeal tween 80 agar

what is the agar used for the ID of yeast to genus and species?

carbohydrate assimilation/fermentation

if an organism is germ tube negative and lacks a capsule, then perform _____

assimilation

growth/pH change positive for _____

fermentation

bubbles (not color change) are positive for _____

c. albicans

which candida species is green on the CHROMagar?

c. tropicalis

which candida species is metallic blue on the CHROMagar?

c. krusei

which candida species is pink and fuzzy on the CHROMagar?

c. kefyr, c. glabrata

which candida species is mauve brown on the CHROMagar?

candida albicans

microscopic: pseudohyphae form with clusters of round blastoconidia at the septa, large chlamydoconidia form singly at terminus, germ tube test positive

candida albicans

most common cause of candidiasis, part of normal flora in skin, mouth, vagina, and GI tract

germ tube assay

used for distinguishing c. albicans and c. dubliniensis from c. tropicalis, c. glabrata, and c. krusei

candida glabrata

microscopic: small oval yeast with single budding is seen, no pseudohyphae are formed

candida glabrata

causes infections occurring in the blood stream or urogenital tract and occasionally in the lung, isolates show reduced susceptibility to fluconazole and amphotericin B

candida krusei

microscopic: form pseudohyphae with elongated blastoconidia forming a tree like appearance

candida krusei

causes infections in susceptible patients, innately resistant to fluconazole

candida tropicalis

microscopic: forms blastoconidia singly or in small groups all along the pseudohyphae

candida tropicalis

particularly infectious to immunocompromised patients, especially virulent in patients with leukemia or similar malignancies

candida parapsilosis

microscopic: blastoconidia singly or in small clusters, crooked appearance of short pseudohyphae with occasional large hyphal elements

candida parapsilosis

frequently responsible for invasive fungal infections in neonates

candida auris

emerging fungus that presents as serious global health threat

candida auris

often drug resistant, difficult to ID with standard lab methods, and causes outbreaks in healthcare settings

cryptococcus neoformans/gattii

colony: produces brown colonies on birdseed agar

cryptococcus neoformans/gattii

microscopic: round and budding, capsules discernable on cornmeal tween agar by spaces between yeast cells

india ink prep

capsules of cryptococcus neoformans are best demonstrated by _____

cryptococcus neoformans/gattii

meningitis is common in HIV/AIDS patients, most common source is pigeon droppings, endemic to pacific northwest of US, causes cryptococcosis

cryptococcosis

a subacute or chronic infection of the CNS but can spread to other sites

rhodotorula

colony: pink to coral or orange to red, sometimes mucois

rhodotorula

microscopic: round budding cells, occasional pseudohyphae and/or capsule

rhodotorula

common contaminant, severe infections in immunocompromised patients with central venous catheters

saccharomyces cerevisiae

microscopic: brewers yeast, round yeast with multi lateral budding

saccharomyces cerevisiae

on special media: forms 1-4 ascospores per ascus, best demonstrated with ascospore stain, kinyoun stain, or gram stain

negative

ascospores are gram _____

saccharomyces cerevisiae

invasive infection in immunocompromised patients receiving pro-biotic treatment of the subtype boulardii for prophylaxis or treatment of antibiotic associated diarrhea

geotrichum candidum

microscopic: coarse true hyphae that segment into rectangular arthroconidia that vary in length, these rectangular cells germinate from one corner, biochemical tests and the absence of blastoconidia

geotrichum candidum

role in infection is uncertain, seems to only cause disease primarily in the lungs of severely immunocompromised patients

trichosporon

microscopic: arthroconidia form on older cultures, presence of pseudohyphae and blastoconidia differentiates this from geotrichum

trichosporon

on cornmeal tween 80 agar at 25 C for 72 hrs, true hyphae and pseudohyphae with blastoconidia singly or in short chains

trichosporon

cause white piedra, a superficial infection of the hair characterized by relatively soft, white nodules located along the shafts of hair

trichosporon

organisms considered normal flora of the skin, nails and mouth

because of shared antigen, sera from patients with disseminated infection may give positive reactions with the cryptococcal antigen latex test

malassezia

colony: require long chain fatty acids for growth, olive oil

malassezia

microscopic: yeast like cells that are phialides with small collarettes, cells are round at one end and cut off at the other end where wide buds form

malassezia

part of normal flora, etiologic agent of pityriasis (tinea) versicolor characterized by pale or dark patches of skin, folliculitis

prototheca

classified as an algae but cause mycosis like infections and often mistaken for yeast

prototheca

microscopic: sporangia of various sizes containing sporangiospores with no budding or hyphae

prototheca

infections may arise subcutaneously through traumatic implantation, causes protothecosis