Isolation and characterization of Escherichia coli O157 : H7 from retail meats in Argentina

Between February and May 2000, 279 meat samples were collected from 136 ret ail stores in Gualeguaychu City, Argentina. Samples were assayed for Escher ichia coli O157:H7 by selective enrichment in modified EC broth containing novobiocin, followed by immunomagnetic separation (IMS) and plating onto bo th sorbitol MacConkey agar supplemented with cefixime and potassium telluri te and a chromogenic medium. Eleven E. coli O157:H7 isolates were detected in 6 (3.8%) of 160 ground beef samples, in 4 (4.8%) of 83 fresh sausages, a nd in 1 (3.3%) of 30 dry sausages. E. coli O157:H7 was not isolated from fi ve hamburger patties or one barbecue-type fresh sausage assayed. The isolat es were tested for virulence-related genes. Ten additional Shiga toxin-prod ucing E. coli (STEC) O157:H7 isolates of food origin, recovered from differ ent locations in Argentina, were included for comparison purposes. All 21 i solates harbored both eae and EHEC-hlyA genes, and 12 (57.1%) encoded stx2/ stx2vh-a. The isolates were of phage types 87 (seven strains), 14 (four str ains), 4 (three strains), and 26 (one strain). Six strains were nontypable by phage typing. Pulsed-field gel electrophoresis (PFGE) revealed 19 XbaI-P FGE profiles. Fifteen (71%) strains were grouped in four clusters. which sh ared more than 80% of DNA restriction fragments. The enrichment culture met hod with IMS was a sensitive procedure to detect E. coli O157:H7 strains in retail meats. Some of the isolates from different stores presented a high clonal relatedness, as determined by XbaI-PFGE and phage typing, and harbor ed the virulence factors associated with human illness.