THE ISOLATION of dermatophytes from clinical materials frequently is complicated by contamination of culture tubes with bacteria and saprophytic fungi. Such specimens as human toenails and the hairs of domestic animals offer a special problem, owing to the presence of large numbers of these contaminants.
Bacterial contaminants are generally controllable by the use either of an acid medium, such as Sabouraud dextrose agar at pH 5.5, or of antibacterial antibiotics, or both. Sabouraud dextrose agar at pH 5.5 fortified with penicillin (20 units per milliliter) and streptomycin (40 units per milliliter) has been used routinely at the Mycology Laboratory of the Communicable Disease Center for the isolation of dermatophytes from clinical materials. The frequent occurrence of saprophytic fungi, however, necessitates inoculation of a large number of tubes for each specimen, and repeated subcultures often are needed to separate a suspected dermatophyte colony from growths of the more rapidly developing saprophytes.
GEORG LK. USE OF A CYCLOHEXIMIDE MEDIUM FOR ISOLATION OF DERMATOPHYTES FROM CLINICAL MATERIALS. AMA Arch Derm Syphilol. 1953;67(4):355–361. doi:10.1001/archderm.1953.01540040013003