Dermatophyte Test Medium is used for the selective isolation of dermatophyic fungi.
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.
