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, lpf(O113), 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 stx(2c) (56.7%), and among 11 O174:H28 strains, the most prevalent was stx(2a) (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 lpf(O113) (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%), lpf(O113) (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.