Virulence traits and different nle profiles in cattle and human verotoxin-producing Escherichia coli O157:H7 strains from Argentina

Abstract

Verotoxin-producing E. coli (VTEC) O157:H7 is the dominant serotype isolated from patients with HUS and, Argentina has the highest rate of HUS in the world. Molecular typing had allowed to identify subpopulations related to the origin and virulence of O157:H7 strains. Our aim was to perform a genetic characterization of 43 O157:H7 strains isolated in Argentine mostly from cattle and humans in order to establish the potential public health risk. For it, we used a combination of molecular subtyping methods in order to identify clade 8_rhsA (C3468G), LSPA-6 and virulence profiles and, a cytotoxicity assay on Vero cell. All isolates carried the clade 8 SNP variant and 98% of them belonged to lineage I/II (2% lineage II). Isolates were grouped into eleven nle profiles, 46% were positive for all nle genes, while the remaining isolates, except two, showed incomplete OI-71, particularly lacked nleF. All isolates showed the plasmid profile ehxA-espP-katP-stcE and harbored ehaA, elfA, iha and lpfA variants lpfA1-3 and lpfA2-2 and, ECSP_0242. The frequencies of the remaining ECSP genes were 95% ECSP_2687, 88% ECSP_3286, 86% ECSP_3620, 53% ECSP_2870/2872 and 44% ECSP_1733. All O157:H7 strains, except the isolate identified as lineage II, were cytotoxic on Vero cells. Among Argentinean strains, most genetic markers occur at equal relative frequencies among clinical and bovine isolates, showing diversity mostly in nle genes profiles. The belonging of the isolates to hypervirulent clade 8 and lineage I/II, the high prevalence of nle and putative virulence factors genes, would allow assigning most O157:H7 strains of this region a high risk to public health.