Fungi III - Yeasts

CRYPTOCOCCUS NEOFORMANS

Cryptococcus neoformans is an encapsulated yeast (non-dimorphic) in pigeon droppings that causes meningoencephalitis, especially in AIDS patients; characteristic halos on India ink stain. Diagnosis is based on two things: cryptococcal antigen (use latex agglutination test to detect capsular polysaccharide antigen); culture on Sabouraud's agar. Treat with Amphotericin B and flucytosine, 2 weeks, followed by fluconazole, 8 weeks.

It produces phenol oxidase, producing melanin and neutralizing neutrophil-released peroxides.

CANDIDA ALBICANS

Candida is normal flora (normal host defense: normal flora, T-cell function). Candida forms pseudohyphae at 20C, and germ tubes at 37C.

Non-immunocompromised.

Oral thrush. Treatment: Imidazole lollipop, nystatin (which can only be given orally).

Vaginitis (pruritus, copious discharge, cottage cheese on vaginal wall). Treatment: Single dose oral fluconazole Risk factors: High pH, diabetes, antibiotic use

Diaper rash in babies, or other warm, moist areas (under breasts).

Immunocompromised.

Esophagitis (risk factors: neonate, steroids AIDS, diabetes).

Disseminated disease (any organ). If you see Candida in blood (always abnormal), look for it on retina (white fluffy patches). There's no good antigen (though beta-D-glucan is sometimes used) or antibody test, but you can diagnose by culture.

**Mucocutaneous candidiasis: lack of dectin, a receptor for glucan that stimulates immune response to fungi. Get granulomatous lesions of fingers, toes, mouth.