Virulence properties and clonal structures of strains of Escherichia coli O119 serotypes

A total of 110 Escherichia coli strains of serogroup O119 were examined for the presence of virulence properties characteristic of enteropathogenic E. coli (EPEC). Three virulence patterns were distinguished based on the detection of a chromosomal gene mediating intimate attachment (eaeA) and plasmid DNA involved in localized adherence (EAF and bfpA). The first pattern, represented by strains which hybridized with three gene probes, was the most common (68%) and, with a single exception, included only O119:H6 strains. Of these strains, 90% showed a typical localized adherence (LA) pattern in HEp-2 cells and 96% were positive for intimate attachment in a fluorescent-actin staining test with a 3-h incubation period. The second pattern was represented by strains which hybridized with the eaeA gene only. Most (89.5%) of these strains showed the LA phenotype but only after 6 h of incubation (LA-like phenotype). The third pattern consisted of strains which were positive for eaeA and bfpA but did not hybridize with the EAF probe. Most (80%) of these strains exhibited the LA-like phenotype. Analysis of several eaeA⁺ bfpA⁺ strains for the expression of the pilin subunit (BfpA) of the bundle-forming pili demonstrated that all LA strains expressed BfpA whereas the LA-like strains did nut. The study of the clonal relationships, carried out by multilocus enzyme electrophoresis in 79 representative strains, defined 11 distinct electrophoretic types (ETs). ET1 included 66% of the strains, most of which displayed the eaeA⁺ bfpA⁺ EAF⁺ pattern and were serotyped as O119:H6 or O119:H. The remaining 10 ETs were each represented by no more than five strains and, with the exception of ET8, included strains of a single serotype. The genetic relatedness of the ETs revealed two main clusters, with most strains in cluster A having the eaeA⁺ bfpA⁺ EAF⁺ combination and a O119:H6 serotype. Cluster B was represented by atypical EPEC strains with only the eaeA⁺ and the eaeA⁺ bfpA⁺ virulence pattern.