Plasmid virulence profiles of verotoxigenic Escherichia coli isolated in Argentina

Abstract

Introduction and Objectives: The verotoxigenic Escherichia coli(VTEC) group is very diverse, being E. coli O157:H7 the most commonserotype associated with sporadic cases and large outbreaks ofhemolytic uremic syndrome in many countries. However, there isgrowing concern about the risk to human health associated withnon-O157 VTEC serotypes. All clinical isolates of E. coli O157:H7possess a large putative virulence plasmid called pO157 and similarplasmids are commonly found in non-O157 VTEC strains, presentinga considerable variability.Material and Methods: We have characterized a total of 208 VTECisolates from Argentina belonging to 49 serotypes, collected fromcattle, foods and humans, for the presence of plasmid-encodedgenes: epeA (serine-protease), espP (extracellular serine protease),katP (periplasmic catalase-peroxidase), stcE (zinc metalloprotease)and subA (subtilase cytotoxin). The epeA gene was detected by amonoplex PCR and the remaining ones, by a pentavalent PCR assaythat also detects ehxA. The isolates had been analyzed in relation toother plasmid-encoded genes, ehxA and saa, in previous studies.Results: The most commonly detected gene was espP, which waspresent in 182 (87%) of the VTEC strains tested. The gen katP wasfound in 36 strains (17%) whereas epeA, subA and stcE were presentin frequencies ranging from 7% to 12%. The ehxA gene, present in47% of the isolates, was usually detected in combination with otherplasmidic genes. Those strains that were positive for subA harboredneither stcE nor katP; stcE was present only in O157:H7 strains, andkatP never appeared simultaneously with saa. Taking into accountthe seven encoded-plasmid genes, 12 virulence profiles wereobserved, being espP+ the most prevalent one (98 isolates), whereaskatP+espP+ehxA+ (22 isolates) prevailed among VTEC isolatesbelonging to O26:H11, O38:H39, O118:H16, O145:NM, O146:NM,O165:NM and O177:NM serotypes. Some serotypes presented onlyone plasmid profile whereas others, such as O20:H19, showed up tofour different profiles. The profile katP+espP+stcE+ehxA+ was onlypresent in O157:H7 isolates and in nine VTEC isolates it was notpossible to detect any of the seven plasmidic genes.Conclusions: In synthesis, our results show that VTEC strains canpossess different combinations of plasmid-encoded virulence genes and even strains belonging to the same serotype can differ in relationto their plasmid genetic composition.