Role of the ehxA gene from Escherichia coli serotype O82 in hemolysis, biofilm formation, and in vivo virulence

Enterohemorrhagic Escherichia coli (EHEC) strains cause serious gastrointestinal disease, which can lead to potentially life-threatening systemic complications such as hemolytic uremic syndrome. Although the ehx gene is established as a major virulence factor of EHEC, the role of this gene in colonization and biofilm formation remains to be elucidated. We constructed recombinant isogenic mutants of the ehxA locus of E. coli HLJ1122 (serotype O82) using the lambda Red homologous recombination system. Significantly higher levels of adherence to human epithelial cells (HEp-2) cells were observed for strain HLJ1122 compared with the mutant strain HLJ1122-Delta ehxA (P < 0.05). Strain HLJ1122 also exhibited significantly higher levels of biofilm formation than strain HLJ1122-Delta ehxA (P < 0.05). Mice infected with strain HLJ1122 showed severe destruction of the intestinal and gastric mucosa; in contrast, mice infected with HLJ1122-Delta ehxA showed limited intestinal pathology, displaying minimal inflammatory infiltrates compared with mock-infected mice. These results showed the multifunctional role of Ehx in E. coli virulence.