Dermatophyte Test Medium (DTM) is a selective and differential culture medium used for the isolation and identification of dermatophyte fungi from clinical and environmental samples. Each sterile petri dish contains approximately 20mL of nutrient agar enriched with proteins and selective antimicrobial agents that suppress bacterial growth and many non dermatophyte fungi. The medium also contains a phenol red pH indicator that changes color when dermatophytes metabolize protein substrates and release alkaline by products. This metabolic activity shifts the medium from yellow to red around the colony, allowing rapid presumptive identification. Dermatophyte Test Medium is widely used in clinical laboratories, veterinary diagnostics, and environmental investigations to detect organisms responsible for infections of skin, hair, and nails.