Genotypic characterization of verotoxigenic Escherichia coli O157:H7 from Argentina

Abstract

Molecular typing has allowed identify different subpopulations related to the origin and virulence of O157:H7 strains. Furthermore, it in combination with analysis of different virulence factors would allow establishing the potential for public health risk that represents a strain.Our aim was to perform a genetic characterization of an O157:H7 population from Argentina by clade and lineage typing and to analyze the distribution of virulence factors to contribute to the knowledge of virulence of the circulating strains. A total of 43 O157:H7 strains isolated in Argentine pampa region from cattle, humans and food were analyzed. The identification of strains belonging to clade 8 was performed by detecting a SNP located in rhsA (PCR-RFLP) and the lineage type, by a six-marker assay (LSPA6). In relation to virulence factors, the following genes were amplified: non-LEE effector genes (nleA, nleH1-2, nleF, nleG, nleG2-1 and nleG9 (OI-71), nleB, nleE and ent/espL2 (OI-36), nleB2, nleC, nleH1-1 and nleD (OI-122) and nleG2-3, nleG5-2, nleG6-2 (OI-57), plasmid-encoded genes (ehxA, epeA, espP, katP, stcE, subAB) and putative virulence genes (ECSP_0242, 1773, 2687, 2870/2872, 3286 and 3620).All isolates belonged to clade 8 and most of them to lineage I/II (98%). Isolates were grouped into six nle profiles, 61% 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 carried ECSP_0242. The frequencies of the remaining ESCP genes were 95% ECSP_2687, 88% ECSP_3286, 86% ECSP_3620, 53% ECSP_2870/2872 and 44% ECSP_1733.According to our results, O157:H7 strains circulating in this Argentine region are a homogeneous group in relation to clades and lineage assignment. 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.