High occurrence of Shiga toxin-producing Escherichia coli (STEC) in healthy cattle in Rio de janeiro State, Brazil

In order to evaluate the prevalence of Shiga toxin-producing Escherichia co li (STEC) strains, 197 fecal samples of healthy cattle from 10 dairy farms, four beef farms and one slaughterhouse at Rio de Janeiro State, Brazil, we re examined for Shiga toxin (Stx) gene sequences by polymerase chain reacti on (PCR). For presumptive isolation of O157:H7 E. coli, the Cefixime-potass ium tellurite-sorbitol MacConkey Agar (CT-SMAC) was used. A high occurrence (71%) of Stx was detected, and was more frequently found among dairy cattl e (82% vs. 53% in beef cattle), in which no differences were observed regar ding the age of the animals. Dot blot hybridization with stx1 and stx2 prob es revealed that the predominant STEC type was one that had the genes for b oth stx1 and stx2 in dairy cattle and one that had only the stx1 gene for b eef cattle. Three (1.5%) O157:H7 E. coli strains were isolated from one bee f and two dairy animals by the use of CT-SMAC. To our knowledge, this is th e first report of O157:H7 isolation in Brazil. A PCR-based STEC detection p rotocol led to the isolation of STEC in 12 of 16 randomly selected PCR-posi tive stool samples. A total of 15 STEC strains belonging to 11 serotypes we re isolated, and most of them (60%) had both stx1 and stx2 gene sequences. Cytotoxicity assays with HeLa and Vero cells revealed that all strains exce pt two of serotype O157:H7 expressed Stx. The data point to the high preval ence of STEC in our environment and suggest the need for good control strat egies for the prevention of contamination of animal products. (C) 1999 Else vier Science B.V. All rights reserved.