[Characterization of enterobacteria producing the broad-spectrum antibiotics microcins]

As a result of screening among 11956 enterobacteria strains isolated from feces of normal children, grown-ups and lambs, seven active microcin-producing strains were obtained. The microcins were shown to be peptides or their derivatives with a low molecular weight (less than 10,000) and a broad spectrum of activity, mainly against gram-negative bacteria. According to cross immunity criteria the microcins studied belonged to two different types. Those of type I could be further classified into two subtypes on the account of difference in the spectrum of antibacterial activity. In 5 cases out of 7 the microcin-producing ability and immunity to microcins have been attributed to plasmids that the strains harboured. The effect of microcins on sensitive cells depended on ompR and ompF gene products.