Abstract
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.
Highlights
Shiga toxin-producing Escherichia coli (STEC) refers to an E. coli pathotype capable of producing either Shiga toxin 1 (Stx1), Shiga toxin 2 (Stx2), or both toxins
The majority of non-O157 STEC strains that are a threat to human health are associated with six specific serogroups (i.e., O26, O45, O103, O111, O121, and O145)
The serotypes O103:H8 and O45:H2 were detected in eight and two goat isolates, respectively; two beef isolates were assigned to serotype O103:H25, and serotype O121:H10 was found in one pork isolate
Summary
Shiga toxin-producing Escherichia coli (STEC) refers to an E. coli pathotype capable of producing either Shiga toxin 1 (Stx1), Shiga toxin 2 (Stx2), or both toxins. STEC has emerged as an important enteric foodborne zoonotic pathogen causing human gastrointestinal disease and has been implicated in sporadic cases and outbreaks of diarrhea, hemorrhagic colitis (HC), and hemolytic uremic syndrome (HUS) worldwide (Smith et al, 2014). STEC O157:H7 has been regarded as the predominant serotype and the main cause of STEC infection worldwide since the early 1980s, recent studies have shown that non-O157 STEC are emerging as important pathogens associated with numerous human infections as well as outbreaks of food-borne illnesses (Johnson et al, 2006; Käppeli et al, 2011). More than 200 non-O157 STEC serotypes have been identified and associated with human illness worldwide (Johnson et al, 2006; Coombes et al, 2008). The public health significance of non-O157 STEC is likely to be underestimated
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