Characterization of Escherichia coli strains producing Shiga Toxin 2f subtype from domestic Pigeon

Shiga toxin-producing Escherichia coli (STEC) can cause mild diarrhea even severe hemolytic uremic syndrome (HUS). Shiga toxin (Stx) is the primary virulence factor. Two Stx types and several subtypes have been identified. STEC strains encoding stx2f (Stx2f-STECs) are frequently identified from pigeons. Stx2f was initially considered to be associated with mild symptoms, more recently Stx2f-STECs have been isolated from HUS cases, indicating their pathogenic potential. Here, we investigated the prevalence of Stx2f-STECs among domestic pigeons in two regions in China, characterized the strains using whole-genome sequencing (WGS), and assessed the Stx2f transcriptions. Thirty-two Stx2f-STECs (4.36%) were culture-positive out of 734 fecal samples (one strain per sample). No other stx subtype-containing strain was isolated. Four serotypes and two sequence types were determined, and a novel sequence type ST15057 was identified. All strains harbored the E. coli attaching and effacing gene eae. Two types of Stx2f prophages were assigned. Stx2f-STECs showed variable Stx transcription levels induced by mitomycin C. Whole genome single-nucleotide polymorphism (wgSNP) analysis revealed different genetic backgrounds between pigeon-derived strains and those from diarrheal or HUS patients. In contrast, pigeon-derived Stx2f-STECs from diverse regions exhibited genetic similarity. Our study reports the prevalence and characteristics of Stx2f-STECs from pigeons in China. The pigeon-derived strains might pose low public health risk.