A survey of Col plasmids in natural isolates of Escherichia coli and an investigation into the stability of Col-plasmid lineages

A survey of colicins in the ECOR reference collection of Escherichia coZi is presented. Twenty-five of the 72 ECOR strains exhibited a phenotype consistent with colicin production and E. coZi isolated from human hosts were more likely to be colicinogenic than those from animal hosts. Multiple representatives of two Col plasmids, low molecular-mass ColEl plasmids and high-molecular-mass, conjugative ColIa plasmids were isolated from the ECOR collection and were examined with a combination of restriction fragment and Southern analysis. These data suggested that ColEl plasmids comprise a stable (cohesive) plasmid lineage, while ColIa plasmids represent a family of distinct plasmid lineages united by the presence of the colicin Ia operon.