Isolation and characterization of non-O157 Shiga toxin-producing Escherichia coli (STEC) isolated from retail ground beef in Santiago, Chile

Shiga toxin-producing Escherichia coli (STEC) is one of the main cause of foodborne disease worldwide, but isolation rates or characteristics of this bacteria from ground beef in Chile are unknown. The present study aimed to isolate and characterize non-O157 STEC from ground beef sold at retail in the city of Santiago, Chile. We analyzed 430 ground beef samples for the presence of STEC, and isolated the microorganism in 10% of samples (43/430). We obtained 56 isolates from the 43 positive samples; 55 of these (98.2%) fermented sorbitol. Most isolates (98.2%; 55/56) showed β-glucoronidase activity, and only six (10.7%; 6/56) were resistant to tellurite. Among the virulence factors studied (stx1, stx2, eae, and hlyA), stx2 was the only virulence factor in 41% of the isolates (23/56), whereas 10.7% (6/56) of isolates carried a combination of three virulence factors (stx1 + stx2 + hlyA). None of the isolates carried the gene eae. Finally, isolates were neither serogroups O157 nor “big six”. In conclusion, ground beef sold in Santiago, Chile is contaminated with STEC; however, further studies are required for understanding their virulence potential.