Opportunistic Yeasts in Clinical Microbiology II

Opportunistic Yeasts

Common fungi causing infections in immunocompromised individuals: C. neoformans and C. albicans

Part of normal flora of mucus membraines

Candida albicans

Major pathogen causing various infections, part of normal flora.

Cryptococcus neoformans

Pathogen associated with pulmonary infections and immunosuppression.

Blastoconidia

Asexual reproduction form produced by budding yeasts.

Pseudohyphae

Tubular structures without septa just contstriction, seen in some yeasts.

Hyphae

Filamentous structures formed by some yeast species.

Germ Tube

Tubular out-pouching used for yeast species identification. C. albicans is positive

Candidiasis

Infection caused by Candida species; opportunistic in immunocompromised pts., diabetics, and antibiotics

Azoles

Class of antifungal drugs effective against yeast infections.

Amphotericin B

Potent antifungal used for severe fungal infections.

Cornmeal Agar

Medium enhancing conidia formation for Candida differentiation.

CHROMagar

Differential media showing color changes for Candida species.

Birdseed Agar

Medium for Cryptococcus neoformans, produces dark colonies.

India Ink

Staining method to visualize capsules around yeasts, especially C. neoformans which makes black colonies

Serological Tests

Detect capsule antigen in body fluids for diagnosis.

Latex Agglutination

Test indicating infection via detectable capsule antigen.

Phenol Oxidase

Enzyme converting phenolic compounds to melanin in Cryptococcus.

Geotrichum candidum

Causes geotrichosis, wound infections, skin lesions, and thrush; part of normal flora and produces arthroconidia.

Pneumocystis jiroveci

Yeast causing Interstitial Plasma Cell Peumonia, especially in immunocompromised patients; cannot be cultured

Carbohydrate Utilization

Testing method to differentiate yeast species based on growth.

Rapid Urease Test

Identifies urease production to differentiate yeast species.

C. albicans

NF of mouth, GI, and urogenital tract

Diseases: thrush, UTI, vaginitis, diarrhea

C. albicans colonies

white to cream colored, smooth, creamy, extensions or "feet" around perimeter

C. albicans Microscopic Morphology

Blastoconidia, pseudohyphae, true hyphae, chlamydoconidia, germ tubes

C. glabrata

UTIs commonly in the immunocompromised but also NF

C. glabrata colonies

Pinpoint, white, smooth colonies showing growth in 72 hrs

C. tropicalis

Long pseudohyphae with blastoconidia causing candidemia and fungal sepsis

C. dubliniensis

Highly associated with HIV+ pts.

Similar to C. albicans but more SEVERE

C. krusei

Long blastoconidia on tree-like branches of pseudohyphae; multidrug resistant in immunocompromised

Crytococcosis

A pulmonary infection that disseminates in the blood

C. neoformans

Present in bat or bird droppings, pigeon poo, decaying plants, and milk

C. neoformans diagnosis

Macroscopic: large, tan, mucoid, black on birdseed

Microscopic: large, round, budding yeast