Molecular markers (SNPs and Shiga toxin types) and Shiga toxin expression in potentially hypervirulent Escherichia coli O157:H7 strains isolated from cattle in Argentine?

NATALIA AMIGO; MARIANO LARZÁBAL; DANIEL A VILTE; ELSA C MERCADO; MANNING SHANNON; ANGEL A. CATALDI

Rosario

Congreso; IX Congreso Argentino de Microbiología General SAMIGE; 2013

Enterohemorragic Escherichia coli (EHEC) O157:H7 is the cause of hemolytic uremic syndrome (HUS), which mainly affects children under 5 years. Argentina is the country with the highest incidence in the world, although factors that contribute to this prevalence are poorly understood. Shiga toxin (Stx) is the main virulence factor of EHEC. Several subtypes of Stx are produced and any of those types are required for the development of HUS. Cattle are the main reservoir and source of infection. Previously SNP typing was used to define nine EHEC O157:H7 distinct clades. Clade 8 strains were more frequently isolated form HUS cases relative to strains of other clades. In Argentina clade 8 strains have been identified in cattle from Santa Fe, La Pampa and Buenos Aires provinces. In this work, 10 isolates of EHEC O157:H7 from cattle in Argentina were studied. Detection of stx1, stx2 and eae genes was performed by PCR. Stx2 subtypes were determined by PCR-RFLP. Clades were determined by SNP typing and the stx2 insertion site was determined by PCR. All strains had eae and stx2 genes. Three strains presented the stx2c (vh-b) variant, one strain had the stx2EDL variant and six strains carried both stx2 and stx2c (vh-b) genes. Only one strain carried the stx1 gene. Six of the isolates were classified as clade 8 by screening for PCR of four SNPs, only two were confirmed to be clade 8 by screening for PCR of 32 SNPs. The remaining four strains had new SNP profiles representing novel genotypes. Five strains showed the insertion site for stx2 in the yehV locus. High levels of Stx were produced by five strains, according to Ridascreen ELISA Kit and two of them showed increased levels of Stx expression in the presence of mitomycin C. Strain 125/99 delta-stx2 was not detected the presence of Shiga toxin. These results show that Argentinean cattle carry strains from multiple lineages, including clade 8, wich was previously, found to be associated with HUS, as well as lineages unique to this population. These results may partially explain the high incidence of HUS in Argentina.