Tyrothricin is a polypeptide antibiotic mixture produced by B. brevis. Tyrothricin is a mixture of tyrocidine and gramicidin that has rapid in vitro bactericidal activity against T. microdentium, T. macrodentium, T. vincentii, T. buccalis, T. mucosum, T. vaginalis, T. cruzi, and L. tropica. Preclinical studies demonstrate that intravenous use of tyrothricin leads to hemolysis-induced lethality (LD50s = 0.4 and 0.3 mg/kg, in dogs and mice, respectively) and damages liver, kidney, and olfactory tissues. Formulations containing tyrothricin are used topically to treat bacterial skin infections.