Abstract: Antibiotic A-39183 complex, comprising microbiologically active, related factors A, B, C, D, and E, is produced by submerged, aerobic fermentation of a new microorganism Streptomyces sp., NRRL 12049. The A-39183 antibiotics are closely related antibiotics. The individual A-39183 factors are separated by chromatography. The A-39183 factors are antibacterial agents which have activity against Staphylococcus and Streptococcus species that are penicillin resistant. The A-39183 factors are also active against both gram-positive and gram-negative anaerobic bacteria, and are ionophores.