Xanthomycins A and B, new antibiotics produced by a species of Streptomyces.

Two new antibiotics have been obtained from culture filtrates of an unidentified species of Streptomyces. These antibiotics are of special interest because of their high potency and their extreme toxicity. Because they are yellow in color and are produced by a Streptomyces, they have been named xanthomycin A and xanthomycin B. The organism, designated Streptomyces 94, is one of a series isolated from oats, flax, and wheat. Because Streptomyces 94 had shown marked antagonistic activity against both Gram-positive and Gram-negative bacteria in a preliminary agar streak test, it was chosen for further study.