The Action of Bacitracin and Subtilin on Treponema pallidum in Vitro and in Vivo.

E"citracin is an antibacterial substance discovered by Johnson, Anker, and Meleney (1945) in culture filtrates of the so-called Tracy strain of Bacillus subtilis. The toxicity of the drug and its absorption and excretion in dogs have been described by Scudi and his coworkers (Scudi and Antopol, 1947; Scudi, Clift, and Krueger, 1947). The blood levels obtained after the intramuscular administration of bacitracin, its urinary excretion, and its renal clearance in rabbits and man have been reported in a previous communication from this laboratory (Eagle, Newman, Greif, Burkholder, and Goodman, 1947). Subtilin is another agent produced by B. subtilis, described by Jansen and Hirschmann (1944). Its antibacterial activity in vitro and in vivo has been studied by Sall6 and Jann (1945). It differs from bacitracin both in its antibacterial spectrum and in its chemical properties. There have been no previous reports about the activity of these two antibiotics in the treatment of syphilis. As will be here reported, both were active in vitro against a cultured strain (Reiter) of Treponema pallidum, bacitracin being considerably more active than subtilin in this respect. In vivo also, bacitracin caused the disappearance of treponemata from testicular chancres in syphilitic rabbits and the prompt healing of the lesions. Subtilin, however, failed to effect permanent healing of the lesions in the largest doses used. The amount of bacitracin necessary to produce a permanent cure in rabbits is under present study, as is its activity in the treatment of the human disease.