Two Enteropathogenic Escherichia coli Strains Representing Novel Serotypes and Investigation of Their Roles in Adhesion

Enteropathogenic (EPEC), which belongs to the attaching and effacing diarrheagenic strains, is a major causative agent of life-threatening diarrhea in infants in developing countries. Most EPEC isolates correspond to certain O serotypes; however, many strains are nontypeable. Two EPEC strains, EPEC001 and EPEC080, which could not be serotyped during routine detection, were isolated. In this study, we conducted an in-depth characterization of their putative O-antigen gene clusters (O-AGCs) and also performed constructed mutagenesis of the O-AGCs for functional analysis of O-antigen (OAg) synthesis. Sequence analysis revealed that the occurrence of O-AGCs in EPEC001 and O132 may be mediated by recombination between them, and EPEC080 and O2/O50 might acquire each O-AGC from uncommon ancestors. We also indicated that OAgknockout bacteria were highly adhesive in vitro, except for the EPEC001 derivative, whose adherent capability was less than that of its wild-type strain, providing direct evidence that OAg plays a key role in EPEC pathogenesis. Together, we identified two EPEC O serotypes in silico and experimentally, and we also studied the adherent capabilities of their OAgs, which highlighted the fundamental and pathogenic role of OAg in EPEC.