In 1969, Taplin, et al. developed Dermatophyte Test Medium for the isolation and recognition of dermatophytic fungi, the causative gent of ringworm from hair, nails and skin. Dermatophyte Test Medium is preferred for isolation and early recognition of Microsporum, Trichophyton and Epidermophyton genera because of a distinct color change in the medium. Rapidly growing species may produce a complete color change in the medium in three days. The slower growing species will change the indicator in longer time periods. Other organisms may grow. These can be recognizes as nondermatophytes by lack of color change. A few organisms, including saprophytes, yeasts and bacteria are capable of changing the medium from red to yellow. These are easily recognzied by their distinctive colonial morphology.

Soy Peptone provides nitrogen and vitamins required for organism growth. Dextrose is included as an energy source. Phenol Red is the pH indicator used to detect acid production. Cycloheximide inhibits most saprophytic molds. The supplements, Gentamicin and Chlortetracycline, aid in selectivity of Dermatophyte Test Medium. Gentamicin inhibits gram-negative bacteria including Pseudomonas spp.. Chlortetracycline is a broad-spectrum antibiotic, inhibiting a wide range of gram-positive and gram-negative bacteria. Agar is the solidifying agent.

Suspend 40.7 grams of the powder in IL of purified water. Mix thoroughl. Heat wih frequent agitation and boil for 1 minute to dissolve the powder completely. Dispense into appropriate containers, loosen caps and autoclave for 15 minutes at 121ºC (15psi). Cool to 50°C. Aseptically add sterile gentamicin (0.1g/L) and sterile chlortetracycline (0.1g/L).

Store powdered media at RT. Stable for 12 months after receipt. Opened bottles should be capped tightly and kept in a dark, low humidity environment. Prepared media should be kept at 4°C and used within a short period of time.