Evaluation of SOC for the presumptive identification of Candida albicans and Cryptococcus neoformans

Abstract

SOC, a fungal growth medium composed of Solryth^R, oxgall, and caffeic acid, was evaluated as a medium to provide rapid, differential identification of Candida albicans and Cryptococcus neoformans. Using a variety of common isolation media to produce the yeast inocula, the germ tube methods tested ranked in the following order of decreasing sensitivity: SOC (97%±1), serum (92%±5), rabbit coagulase plasma with EDTA in combination with tryptic soy broth (89%±5), TOC (89%±6), and rabbit coagulase plasma with EDTA (83%±4). In chlamydospore production, SOC also proved to be the most sensitive after 24 h incubation: SOC (96%±2), TOC (80%±2), and cornmeal-Tween 80 agar (14%±3). Other medically important yeasts showed normal patterns of growth within 24 h on SOC, thus assisting in their identification.Eighty strains of Cryptococcus neoformans showed characteristic brown pigmentation on SOC and TOC within 18 h, while all other species of the genus Cryptococcus and 229 Candida isolates did not show a change in pigmentation.