The laboratory diagnosis of dermatophytosis complicated with Candida albicans

Abstract

When scrapings of skin and nails containing Candida albicans and a dermatophyte are cultured, the more rapidly growing C. albicans may prevent the growth of the dermatophyte. Studies have shown that C. albicans has a complete requirement for biotin but the common dermatophytes such as Trichophyton rubrum and T. mentagrophytes and Epidermophyton floccosum are able to produce their requirements of this growth factor when cultured on a suitable medium in which the biotin has been inactivated. Advantage has been taken of this to restrict the growth of C. albicans by inactivating with egg albumen the biotin naturally present in the culture medium. The active principal in egg albumen is avidin.To further discourage the growth of C. albicans and encourage the growth of a dermatophyte, erythritol was used in place of dextrose in the isolation medium. This carbohydrate is not used by C. albicans but is used by T. rubrum and T. mentagrophytes.The new medium formulated to impede the growth of C. albicans but encourage the growth of a dermatophyte is casamino acids erythritol albumen agar. It minimizes the chance of sending an incomplete and misleading report to the physician.