Dermatophyte Test Medium (DTM) Slants, Modified with Chloramphenicol A 10. Dermatophyte Test Medium (DTM) is a selective and differential medium used for the detection andpresumptive identification of dermatophytes from clinical and veterinary specimens. Because of theunavailability of one of the inhibitory agents, chlortetracycline, Dermatophyte Test Medium (DTM),Modified with Chloramphenicol is recommended as a substitute for the original DTM formation.