COLICINOGENY AMONG ESCHERICHIA-COLI SEROTYPES, INCLUDING O157-H7, REPRESENTING 4 CLOSELY-RELATED DIARRHEAGENIC CLONES

Twenty-seven diarrheagenic Escherichia coli (DEC) strains from five cl osely related, genetically distinct clones (DEC 3, 4, 8, 9, and 10), r epresenting serotypes commonly associated with Shiga-like toxin produc tion, i.e., O15:H-, O26:(H11, H-), O111:(H8, H11, H-), and O157:H7, we re evaluated for colicinogeny on Luria agar or Luria agar containing 0 .25 mu g/ml mitomycin C to induce colicin production. Ten (37%) of the DEC strains tested were colicinogenic. One of 11 serotype O157:H7 str ains, DEC strain 4E, produced a colicin identified as Col D. DEC strai ns 8B, 9D, and 10B produced Col El, whereas DEC strain 10A produced Co l E2. DEC strains 8A, 8E, 10C, 10E, and 10F produced ''untypable'' col icins that killed almost all Pugsley Colicin Reference Set strains and the other DEC strains tested. To aid with further characterization of the colicins, plasmids extracted from each colicin-producing (Col(+)) DEC strain were used to transform E. coli strain DH5 alpha. All Colt DH5 alpha transformants contained one plasmid ranging in size from 1.3 to 10 kb. Some transformants were stable colicin producers whereas ot hers were unstable. The inhibitory activity and colicin sensitivity an d insensitivity profiles of the Colt transformants were similar to tho se of the corresponding Col(+) donor DEC strains. It appears that the untypable colicins are novel and, thus, warrant further study. Colicin production by some of the DEC strains evaluated partly explains why t hey were insensitive to standard colicins in a previous study.