Isolation and characterization of Escherichia coli strains producing microcins of B and C types

A screening of 11956 enterobacteria isolates resulted in selection of seven active microcin-producing strains. The microcins were shown to be peptides or their derivatives with a rather broad spectrum of activity, mainly against Gram-negative bacteria. According to cross-immunity criteria, the microcins studied belonged to two of the previously suggested types, B (five strains) and C (two strains). Those of type B could be further classified into two subtypes on the account of differences in the spectrum of antibacterial activity. In five cases out of seven the microcin-producing ability has been attributed to plasmids that the strains harboured. The effect of microcins on sensitive cells was shown to depend on ompR and ompF gene products.