Genetic diversity of the enterohaemolysin gene (ehxA) in non-O157 Shiga toxin-producing Escherichia coli strains in China

Non-O157 Shiga toxin-producing Escherichia coli (STEC) is increasingly recognized as an important enteric foodborne pathogen. The hallmark of the disease is the production of Shiga toxins; however, there are other virulence factors that contribute to the pathogenesis of STEC. This study aimed to investigate the prevalence and genetic diversity of the enterohaemolysin gene, ehxA, among non-O157 STEC strains from human, animal, and food sources. The ehxA gene was amplified from 138 (31.8%) of 434 non-O157 STEC strains, among which 36 unique ehxA sequences were identified. Based on ehxA sequence analysis, three phylogenetic ehxA groups (I II, and III) were determined. Correlations between ehxA groups and sources, serotypes, and virulent gene profiles were observed. The ehxA group II strains were mostly diarrhoeal patient-derived and may demonstrate higher pathogenic potential compared with the ehxA group I and group III strains. Five types of replicons (I1-Ig, FIB, K, F, and B/O) were identified in the 138 ehxA-positive strains, and 3.6%, 5.8%, and 52.2% of the strains harboured toxB, katP and espP genes, respectively, implying marked genetic diversity of ehxA containing plasmids in non-O157 STEC strains. Sequence-based ehxA genotyping might be important in modern strain typing and in epidemiological surveillance of non-O157 STEC infections.