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

ABSTRACT: 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.

SUBMITTER: Fu S

PROVIDER: S-EPMC5844952 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:Shiga toxin-producing Escherichia coli (STEC) causes diarrhea and hemorrhagic colitis with life-threatening complications, such as hemolytic uremic syndrome. The aim of this study was to assess the molecular epidemiologic features of non-O157 STEC strains from different resources in China and illustrate the role of animal reservoirs or animal-derived foodstuffs in human STEC infections. A collection of 301 non-O157 STEC isolates from domestic and wild animals (i.e., cattle, goat, pig, yak, pika, and antelope), raw meats (i.e., beef, pork, mutton, chicken, and duck), diarrheal patients, and healthy carriers in different regions of China were selected in this study. Of the 301 analyzed STEC isolates, 67 serogroups, and 118 serotypes were identified; this included some predominant serogroups associated with human disease, such as O26, O45, O103, O111, and O121. Eighteen different combinations of stx subtypes were found. Eleven isolates carried the intimin gene eae, 93 isolates contained ehxA, and 73 isolates carried astA. The prevalence of other putative adhesion genes saa, paa, efa1, and toxB was 28.90% (87), 6.98% (21), 2.31% (7), and 1% (3), respectively. The phylogenetic distribution of isolates was analyzed by multilocus sequence typing (MLST). Ninety-four sequence types were assigned across the 301 isolates. A subset of isolates recovered from yak and pika residing in the similar wild environments, Qinghai-Tibetan plateau, showed similar genetic profiles and more tendencies to cluster together. Isolates from goat and mutton exhibited close genetic relatedness with those from human-derived isolates, providing evidence that transmission may have occurred locally within intraspecies or interspecies, and importantly, from animal reservoirs, or raw meats to humans. Comparing isolates in this study with highly virulent strains by MLST, along with serotyping and virulence profiles, it is conceivable that some of isolates from goat, yak, or raw meats may have potential to cause human diseases.

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

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