Clonal relationship among invasive and non-invasive strains of enteroinvasive Escherichia coli serogroups

The genetic relatedness among 96 invasive Escherichia coli belonging to sev eral serogroups and 13 non-invasive of several serotypes that share the sam e O antigen was investigated by multilocus enzyme electrophoresis analysis. The invasive strains were isolated in different parts of the world and mos t of them recovered from dysentery. Twenty-nine electrophoretic types were distinguished and the most invasive strains were found to belong to two maj or lineages. These results suggested that the invasive ability in these str ains has evolved in divergent chromosomal backgrounds, presumably through t he horizontal spread of plasmid-borne invasion genes. The maintenance of in vasive phenotypes in separate lineages suggests that this ability confers a selective advantage to invasive strains. (C) 1999 Published by Elsevier Sc ience B.V. All rights reserved.