ISOLATION AND CHARACTERIZATION OF ESCHERICHIA-COLI STRAINS PRODUCING MICROCINS OF B-TYPE AND C-TYPE

A screening of 11956 enterobacteria isolates resulted in selection of seven active microcin-producing strains. The microcins were shown to b e peptides or their derivatives with a rather broad spectrum of activi ty, mainly against Gram-negative bacteria. According to cross-immunity criteria, the microcins studied belonged to two of the previously sug gested types, B (five strains) and C (two strains). Those of type B co uld be further classified into two subtypes on the account of differen ces in the spectrum of antibacterial activity. In five cases out of se ven the microcin-producing ability has been attributed to plasmids tha t the strains harboured. The effect of microcins on sensitive cells wa s shown to depend on ompR and ompF gene products.