New genetic pattern of Escherichia coli O157:H7 biotype "B" in Argentina

Argentina has the highest rate of cases of hemolytic uremic syndrome (HUS) in the world. Outbreaks and sporadic cases of HUS have been associated with O157:H7 Shiga toxin-producer Escherichia coli (STEC). The aim of this study was to compare the genetic diversity and clonal relatedness of Escherichia coli O157:H7 biotype B. Four biotype B strains were isolated from two patients with HUS and two asymptomatic household contacts in the city of Mar del Plata. PCR was performed to detect stx(1), stx(2), rfb(O157), eae, ehxA and fliC(h7) genes, and pulsed-field gel electrophoresis (Xbal-PFGE) to establish the genetic diversity and the clonal relatedness. All strains harbored the stx(2), stx(2c(vh-a)), eae, ehxA and fliC(h7) genes and belonged to phage type 2. By means of XbaI-PFGE, three patterns were identified, showing high clonal relatedness and related to the same event, but there was no established epidemiological link between cases of HUS. These patterns of XbaI-PFGE were new, because they were not included in the database of E. coli O157 in Argentina. Using tools of detection and classification for diagnosis, reference laboratories will be able to detect the emergence of new clones associated with human diseases.