31 terms

Yeasts

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Pneumocystis jirovecii (formerly carinii)
a. Protozoan: Antifungals ineffective; No ergosterol; "Life Cycle"
b. Fungus: Chitin; Ascospores internals; Stains with "fungus" stains
c. Bacterium: Trimethoprim-sulfamethoxazole
d. Different species infect different hosts
e. Nothing in vitro
Pneumocystis jirovecii (formerly carinii)
a. Serology, nucleic acid detection not useful

b. Cyst wall, intracystic body stains
Pneumocystis jirovecii (formerly carinii)
a. 98.4% agreement between toluidine blue (histology) and fluorescent monoclonal antibody (microbiology)

b. 15% sensitivity in a cohort of expectorated and induced sputum specimens collected from AIDS population
Geotrichum spp.
a. Yeast-like mold

b. Debilitated hosts; bronchial manifestations, rare disseminated disease

c. Inhibited by cycloheximide

d. Urease-negative
Prototheca wickerhamii
a. Yeast-like achlorophyllous alga

b. Verrucous cutaneous infections: Olecranon bursitits

c. Sporangia with septations
Black Yeasts
a. Able to produce melanized budding cells at some (early) stage in life cycle

b. Most also produce true mycelium; therefore, identification based on asexual reproduction

c. Many examples within Ascomycota and Basidiomycota; lots of name changes: Exophiala spp., Aureobasidium pullulans, and Hortaea werneckii
Black Yeasts
a. Slow-growing; some are very slow-growing
b. Differential optimum growth temperatures
c. E. jeanselmei: mycetoma & phaeohyphomycosis
d. E. dermatitidis: phaeohyphomycosis & predilection for CNS; ocular
e. H. werneckii: tinea nigra
f. A. pullulans: common contaminant & phaeohyphomycosis
Ustilago Species
a. "Corn smut fungus"

b. Inhaled and subsequently isolated from sputum; rarely implicated in human disease

c. White, pasty, moist, yeast-like at first; becomes tan/brown, mycelial within 20 days
Rhodotorula spp.
a. Proclivity to impact terminal stages of carcinoma and bacterial endocarditis

b. Urease-positive; rare rudimentary pseudohyphae

c. R. mucilaginosa utilizes KNO3; R. glutinis
Sporobolomyces spp.
a. Rare pathogenesis in immunocompromised patients

b. Best growth at 25C

c. Forcible discharge of kidney-shaped ballistoconidia, forms satellite colonies
Malassezia furfur
a. Normal skin flora in more than 90% of adults

b. Tinea versicolor; cradle cap; dandruff: Catheter-related sepsis (neonates, TPN) with secondary pneumonia

c. Optimal recovery of the organism involves acquisition of blood via lipid infusion catheter

d. Grows poorly at 25C; solid medium overlaid with thin layer of olive oil (not for veterinary)
Saccharomyces cerevisiae
a. Typically non-pathogenic

b. Exposure to commercial strains associated with health foods and baking may allow for colonization/infection

c. 1-4 ascospores per ascus
i. Stain Gram-negative (vegetative cells stain Gram-positive)
ii. Stain with Kinyoun stain (vegetative cells visualized with counterstain)
Trichosporon spp.
a. T. beigelii formerly considered main pathogen of genus

b. 19 taxa recognized; nearly all systemic infection caused by six species: T. asahii, T. asteroides, T. mucoides, T. cutaneum, T. inkin, and T. ovoides

c. Neutropenic patients; AIDS; extensive burns; heart valve surgery; catheterized patients
Blastoschizomyces capitatus
a. Obsolete taxa Trichosporon capitatum and Blastoschizomyces pseudotrichosporon
b. Emerging cause of invasive fungal disease in leukemic patients; mortality rate from invasive disease high in neutropenic patients
c. Difficult to delineate from Trichosporon: Urease-negative
d. Growth at 45C
e. Non-fermentative: Growth on cycloheximide
Candida lipolytica
a. Emerging opportunistic pathogen

b. Pseudohyphae and true hyphae bearing elongate blastoconidia form stark branching appearance

c. Urease-positive
Candida lusitaniae
a. Emerging opportunist (malignancy); highly-resistant to amphotericin B

b. Pseudohyphae slender, branched, curved; short chains of elongate blastoconidia
Candida kefyr
a. Rare etiology of systemic disease, cystitis

b. Elongate blastoconidia line up in parallel; "logs in stream"

c. Presence of metallic green sheen on Levine eosin methylene blue (EMB) agar demonstrated 100% positive predictive value for C. kefyr
Cryptococcus neoformans
a. HIV signal disease; cryptococcosis is first AIDS defining illness in 45% of AIDS patients

b. Antecedent lung infection; disseminates to CNS, bone, skin, others

c. CSF cryptococcal antigen sensitivity equals or exceeds that of culture

d. 85.2% sensitivity of Gram stain in culture-positive cases of cryptococcal meningitis
Cryptococcus spp.
a. C. neoformans/gattii complex reclassification (e.g., C. neoformans var. neoformans)
b. Six species may be encountered clinically: C. neoformans, C. albidus, C. terreus, C. uniguttulatus, C. luteolus, C. laurentii
c. Only C. neoformans/gattii complex produces phenol oxidase; "birdseed" agar, also a rapid test utilizing caffeic acid disc
d. Urease-positive; nitrate can help differentiate
North America Candidemia
a. C. albicans
b. C. glabrata
c. C. parapsilosis
d. C. tropicalis
e. C. krusei
Candida krusei
a. Emerging opportunist; constitutively resistant to fluconazole

b. Distinctive morphology on chromogenic medium

c. Urease-positive (some)

d. Elongate blastoconidia, tree-like appearance
Candida Tropicalis
a. In patients with lymphoreticular malignancy or leukemia, more virulent than C. albicans

b. Distinctive morphology on chromogenic medium

c. Blastoconidia singly or in small groups along long pseudohyphae
Candida parapsilosis
a. Infections in particulary susceptible hosts; candidal endocarditis

b. Blastoconidia singly or in small clusters; crooked/curved short pseudohyphae
Candida glabrata
a. Potential induction of fluconazole resistance upon suboptimal treatment
b. Endocarditis, meningitis, multifocal disease
c. 20% of Candida urinary tract infections
d. When compared to colony forming units on blood agar, C. glabrata colony forming units on eosin methylene blue agar are larger
e. Small blastoconidia; may bud at 11:00 and 1:00
f. "Distinctive" morphology on chromogenic medium
g. Rapid trehalose testing gives presumptive ID within 3 hours when correlated with cellular morphology; watch out for blood agar
Candida albicans
a. Normal flora (small numbers) in skin, vagina, oral cavity, intestine

b. As with other Candida spp., immunocompromised patients, those with indwelling catheters, those on broad-spectrum antibacterials most susceptible

c. Diseases: Thrush, Skin infection, Vaginitis, Fungemia, Onychomycosis

d. Finger-like or star-like projections on Blood agar
Candida albicans
a. Most common species isolated from all forms of candidiasis

b. Make sure that germ tube is contiguous (C. tropicalis); considered presumptive

c. Distinctive morphology on chromogenic medium

d. Terminal chlamydoconidia, especially at 25C
Candida dubliniensis
a. Most frequently isolated from oropharynx of HIV-positive patients (pseudomembranous oral candidiasis)

b. Infrequently recovered from blood, urine, vaginal specimens (immunocompromised)

c. Candida albicans mimicry: Germ tube and Chlamydoconidia

d. Commercial germ tube reagent reduces frequency of GT-positive C. dubliniensis
Broth Microdilution
a. Can test variety of yeasts, including Candida spp. and C. neoformans, but not dimorphs
b. Interpretive criteria only for Candida spp.
c. RPMI 1640 broth (MOPS buffer, 0.2% dextrose)
d. 24h Candida growth; 48h C. neoformans Sabouraud dextrose, potato dextrose agar
e. 0.5 McFarland; dilution to final inoculum range of 0.5 x 103 to 2.5 x 103 CFU/mL
f. Fluconazole, 5-fluorocytosine: 0.12-64 mg/mL; Other antifungals: 0.03-16 mg/mL
g. Amphotericin B: observe 100% inhibition; Other agents: observe 50% inhibition
35C Ambient Air
i. 24 hours for echinocandins
ii. 24-48 hours for amphotericin B
iii. 24-48 hours for fluconazole
iv. 48 hours for 5-fluorocytosine
v. 48 hours for other azoles
vi. 70-74 hours for C. neoformans testing
Disk Diffusion
a. Has lagged behind broth dilution
b. Candida versus: Caspofungin, Posaconazole, Fluconazole, and Voriconazole
c. Mueller-Hinton agar with 2% dextrose (0.5 mg methylene blue/mL)
d. 24-hour Candida spp. growth on Sabauroud dextrose agar
e. 0.5 McFarland standard for inoculum of 1 x 106 to 5 x 106 CFU/mL: Caspofungin 5 mg , Posaconazole 5 mg, Fluconazole 25 mg, and Voriconazole 1 mg
f. 35C ambient air; 20-24 hours
g. Observe for prominent reduction in growth: Ignore pinpoint microcolonies at zone edge and large colonies within inhibition zone
Etest
a. Fluconazole, itraconazole, 5-fluorocytosine strips FDA-approved for clinical use

b. Etest MIC data tended to be higher than broth microdilution for fluconazole testing of 1586 Candida spp., but overall agreement 96.4%

c. Etest MIC data tended to be higher than broth microdilution for voriconazole testing of 1586 Candida spp., but overall agreement 98.1%