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

Abstract

Shiga toxin-producingEscherichia 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 subtypecontaining 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 pigeonderived strains might pose low public health risk.Shiga toxin-producing Escherichia coli (STEC) is a significant zoonotic pathogen, which can cause mild diarrhea, gastroenteritis, and even severe life-threatening complication hemolytic uremic syndrome (HUS) in humans 1,2 . The key virulence factor of STEC is Shiga toxin (Stx), an essential factor for the development of HUS 3,4 . The stx gene is located downstream of the Q gene encoding late promotor in lysogenized lambdoid prophages. The transcription and expression of Stx is regulated by the Stx prophages. Stx-converting phages are highly mobile genetic elements that play an important role in horizontal gene transfer and STEC pathogenies 5 .Stx can be distinguished into two immunologically distinct types (Stx1 and Stx2) 6 . Based on variations in amino acid sequences, various subtypes, i.e., four Stx1 (Stx1a, Stx1c, Stx1d, and Stx1e) and fifteen Stx2 (Stx2a to Stx2o) subtypes have been reported 7,8 . Shiga toxin subtypes display notable variances in biological activity, including serological reactivity, receptor binding, and the potency of the toxin. These differences are instrumental in determining the host specificity and the resultant health outcomes after human infection. Stx2a-and Stx2dproducing strains are more often associated with severe disease than Stx1-producing strains 9,10 . Stx2f subtype is highly distinct from other known Stx2 subtypes when comparing nucleotide and amino acid sequences, and this may lead to those most routine tests cannot efficiently identify this subtype 11 , its clinical ...