Putative virulence factors and clonal relationship of O174 Shiga toxin-producing Escherichia coli isolated from human, food and animal sources.

Shiga toxin-producing Escherichia coli (STEC) is th etiological agent of gastrointestinal diseases as haemorrhagic colitis and haemolytic-uraemic syndrome (HUS). Shiga toxin (Stx) is the main virulence factor. There are two types, Stx1 and Stx2, and several subtypes. Other virulence factors are involved in pathogenesis. While O157:H7 is the predominant serotype, at present non-O157 STEC strains are increasingly recognized as foodborne pathogens worldwide. In Argentina, STEC O174 stands out as an emerging pathogen and is one of the four most prevalent non-O157 STEC serogroups. The aim of this study was to characterize 41 O174:[H21, H28] STEC strains isolated from animals, food, and humans. Isolates were characterized by stx genotyping, adhesion factors (afaC, eae, iha, lpfO113 , saa, and toxB), additional toxins (cdtV, ehxA, subA) and clonal relationship by pulsed-field gel electrophoresis (PFGE). Among 30 O174:H21 strains, the most prevalent stx subtype was stx2c (56.7%), and among 11 O174:H28 strains, the most prevalent was stx2a (90.9%). Regarding virulence factors, all strains were positive for afaC gene and negative for eae and toxB genes. In O174:H21, the frequency of additional factors was lpfO113 (96.6%), iha (83.3%), ehxA and saa (10%), and subA (3.3%), meanwhile in O174:H28 strains the frequency was iha and subA (100%), lpfO113 (90.9%), ehxA and saa (90.9%), and cdtV (9.09%). By Xbal-PFGE, 29 patterns were established with 64.01% similarity and three clusters were detected. Given the fact that the O174 serogroup is a local emergent, it is important to study the virulence profiles to understand its potential pathogenicity.