Abstract
Shiga toxin (Stx)-producing Escherichia coli (STEC) is an important foodborne pathogen with the ability to cause bloody diarrhea (BD) and hemolytic uremic syndrome (HUS). Little is known about enterohemolysin-encoded by ehxA. Here we investigated the prevalence and diversity of ehxA in 239 STEC isolates from human clinical samples. In total, 199 out of 239 isolates (83.26%) were ehxA positive, and ehxA was significantly overrepresented in isolates carrying stx2a + stx2c (p < 0.001) and eae (p < 0.001). The presence of ehxA was significantly associated with BD and serotype O157:H7. Five ehxA subtypes were identified, among which, ehxA subtypes B, C, and F were overrepresented in eae-positive isolates. All O157:H7 isolates carried ehxA subtype B, which was related to BD and HUS. Three ehxA groups were observed in the phylogenetic analysis, namely, group Ⅰ (ehxA subtype A), group Ⅱ (ehxA subtype B, C, and F), and group Ⅲ (ehxA subtype D). Most BD- and HUS-associated isolates were clustered into ehxA group Ⅱ, while ehxA group Ⅰ was associated with non-bloody stool and individuals ≥10 years of age. The presence of ehxA + eae and ehxA + eae + stx2 was significantly associated with HUS and O157:H7 isolates. In summary, this study showed a high prevalence and the considerable genetic diversity of ehxA among clinical STEC isolates. The ehxA genotypes (subtype B and phylogenetic group Ⅱ) could be used as risk predictors, as they were associated with severe clinical symptoms, such as BD and HUS. Furthermore, ehxA, together with stx and eae, can be used as a risk predictor for HUS in STEC infections.
Highlights
Shiga toxin-producing Escherichia coli (STEC) is an important enteric foodborne pathogen that can cause bloody diarrhea (BD), hemorrhagic colitis, and potentially fatal hemolytic uremic syndrome (HUS) in infected humans [1]
Shiga toxin and intimin have been widely investigated as vital virulence factors of STEC [21]
Enterohemolysin has emerged as a possible marker for the identification of specific STEC strains, such as O26, O157, O145, and O103, which are highly related to severe clinical symptoms, including BD and HUS [13,17,22,23]
Summary
Shiga toxin-producing Escherichia coli (STEC) is an important enteric foodborne pathogen that can cause bloody diarrhea (BD), hemorrhagic colitis, and potentially fatal hemolytic uremic syndrome (HUS) in infected humans [1]. Shiga toxins (Stx and Stx2) are the main virulence factors of STEC, which can mediate a significant cytotoxic effect in human vascular endothelial cells [7]. At least 15 stx and stx gene subtypes have been identified, among which, stx2a, stx2c, and stx2d are more virulent than other subtypes as they are highly associated with severe clinical outcomes, such as HUS [9]. It is noteworthy that ehxA is prevalent in STEC strains and is closely associated with isolates causing diarrheal disease and HUS [15]
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