An antibiotic with activity against gram-positive bacteria from the gentamicin-producing strain of Micromonospora purpurea

A mixture of polycyclic aromatic compounds with activity against gram-positive bacteria was isolated from a gentamicin-producing species of Micromonospora. A recent publication by Sugawara et al. 1997 reported the isolation of a lipophilic isonitrile gram-positive antibiotic from the fermentation broth filtrate of Micromonospora echinospora subsp. echinospora Y-03559J, a culture also reported to produce gentamicin. In the publication describing the discovery of gentamicin (Weinstein et al. 1963) a lipophilic gram-positive antibiotic was reported to be associated with the non-diffusible mycelial pigment of Micromonospora purpurea, NRRL 2953. Further details were not provided at that time but recent studies, reported here, have shown this lipophilic substance to be a mixture of polycyclic aromatic compounds. Attempts were made to isolate and purify the active component. Fermentation was carded out in a medium composed of 3 g beef extract, 5 g tryptone, 5 g yeast extract, 1 g glucose, 24 g potato starch, 2 g CaCo₃, 1 ml Dow Corning Antifoam type B and tap water. The fermentation was carried out for 5 days at 30°C on a rotary shaker at 240 rpm.