Comparative sequence analysis of the plasmid-encoded regulator of enteropathogenic Escherichia coli strains

Enteropathogenic Escherichia coli (EPEC) strains that carry the EPEC adhere nce factor (EAF) plasmid were screened for the presence of different EAF se quences, including those of the plasmid-encoded regulator (per). Considerab le variation in gene content of EAF plasmids from different strains was see n. However, bfpA, the gene encoding the structural subunit for the bundle-f orming pilus, bundlin, and per genes were found in 96.8% of strains. Sequen ce analysis of the per operon and its promoter region from 15 representativ e strains revealed that it is highly conserved. Most of the variation occur s in the 5' two-thirds of the perA gene. In contrast, the C-terminal portio n of the predicted PerA protein that contains the DNA-binding helix-turn-he lix motif is 100% conserved in all strains that possess a full-length gene. In a minority of strains including the O119:H2 and canine isolates and in a subset of O128:H2 and O142:H6 strains, frameshift mutations in perA leadi ng to premature truncation and consequent inactivation of the gene were ide ntified. Cloned perA, -B, and -C genes from these strains, unlike those fro m strains with a functional operon, failed to activate the LEE] operon and bfpA transcriptional fusions or to complement a per mutant in reference str ain E2348/69. Furthermore, O119, O128, and canine strains that carry inacti ve per operons were deficient in virulence protein expression. The context in which the perABC operon occurs on the EAF plasmid varies. The sequence u pstream of the per promoter region in EPEC reference strains E2348/69 and B 171-8 was present in strains belonging to most serogroups. In a subset of O 119:H2, O128:H2, and O142:H6 strains and in the canine isolate, this sequen ce was replaced by an IS1294-homologous sequence.