Abstract:
Objective To understand the etiological characteristics and potential source of infection of the first Shiga toxin-producing Escherichia coli (STEC) O157:H7 infection case detected through diarrheal syndrome surveillance in Ma'anshan, Anhui province.
Methods A field epidemiological investigation was conducted, and clinical and environmental samples were collected for STEC O157:H7 isolation, culture, and identification. Drug susceptibility testing, Shiga toxin (Stx) induction assays, and whole-genome sequencing (WGS) were performed for the isolated strains. Based on WGS data, Stx subtyping, multilocus sequence typing (MLST), and core-genome single nucleotide polymorphism (cgSNP) phylogenetic analyses were carried out to evaluate the genetic relationship.
Results On December 9, 2024, one strain of O157:H7 STEC strain (stx2+, eae+) was isolated from the stool sample of a child with diarrhea. In 70 environmental and animal samples collected for source tracing, two STEC O157:H7 strains were isolated from chicken feces. The drug susceptibility testing showed that the human isolate and the two chicken-origin isolates were all sensitive to 15 antibiotics. The etiological analysis revealed that all the three isolates shared identical stx2c and eae-γ1 subtypes and belonged to sequence type (ST)11458. The phylogenetic analysis demonstrated that they clustered within the same clonal lineage, with only differences in 7–12 core-genome SNPs, indicating extremely close genetic relationship.
Conclusion The STEC O157:H7 infection might be associated with the exposure to infected poultry or contaminated environment. The isolates carried stx2c subtype and exhibited low toxin induction levels, suggesting relatively low pathogenic potential. This study provides the first evidence of Shiga toxin-producing O157:H7 strains from local poultry has high genetic relationship with clinical human isolate, highlighting that chickens and other poultry might be the potential reservoirs for STEC O157:H7, to which close attention should be paid in future surveillance and source-tracing efforts.
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