Serotypes, virulence genes, and intimin types of Shiga toxin-producing Escherichia coli (STEC) and enteropathogenic E. coli (EPEC) isolated from calves in São Paulo, Brazil.

Shiga toxin-producing Escherichia coli (STEC), is the most important recently emerged group of foodborne pathogens. Ruminants, especially cattle, have been implicated as a principal reservoir of STEC, undercooked ground beef and raw milk being the major vehicles of foodborne outbreaks. Enteropathogenic E. coli (EPEC) strains are defined as eae-harboring diarrheagenic E. coli that possess the ability to form A/E lesions on intestinal cells and that do not possess Shiga toxin genes. In order to determine the occurrence, serotypes and virulence markers of STEC and EPEC strains, 546 fecal samples from 264 diarrheic calves and 282 healthy calves in beef farms in São Paulo, Brazil, were screened by PCR. STEC and EPEC were isolated in 10% and 2.7% of the 546 animals, respectively. Although IMS test was used, the STEC serotype O157:H7 was not detected. The most frequent serotypes among STEC strains were O7:H10, O22:H16, O111:H(-), O119:H(-) and O174:H21, whereas O26:H11, O123:H11 and O177:H11 were the most prevalent among EPEC strains. In this study, serotypes not previously reported were found among STEC strains: O7:H7, O7:H10, O48:H7, O111:H19, O123:H2, O132:H51, O173:H(-), and O175:H49. The eae gene was detected in 25% of the STEC and 100% of EPEC strains. The intimin type theta/gamma2 was the most frequent among STEC, whereas the intimin beta1 was the most frequent intimin type among EPEC strains. To our knowledge, this is the first report of the occurrence of the new intimin muB in one strain of animal origin. This new intimin was detected in one atypical EPEC strain of serotype O123:H? isolated from diarrheic cattle. The enterohemolysin (ehxA) was detected in 51% of the STEC and 80% of the EPEC strains, whereas STEC autoagglutinating adhesin (saa) virulence gene was detected only in those STEC strains negative for eae gene. All 15 bovine EPEC strains isolated in this study were negative for both eaf and bfp genes. Our data shows that in Brazil cattle are not only a reservoir of STEC and atypical EPEC, but also a potential source of infection in humans, since the important STEC serotypes previously described and associated with severe diseases in humans, such as O111:H(-), O113:H21, O118:H16, and O174:H21 were isolated.

Frequency of Shiga toxin-producing Escherichia coli (STEC) isolates among diarrheic and non-diarrheic calves in Brazil.

The occurrence of Shiga toxin (Stx) gene sequences was examined in 344 fecal samples from diarrheic (n=139) and non-diarrheic (n=205) calves from 12 beef farms in São Paulo State, Brazil to study the prevalence of Shiga toxin-producing Escherichia coli (STEC) strains. Forty-four (12.7%) animals were found to be positive for stx. The frequency of carriage of stx was higher in diarrheic calves (28/139, 20%) than in non-diarrheic animals (16/205, 7.8%) (P<0.001). Among the 24 STEC strains recovered from the animals, 12 isolates carried stx1, four stx2, and 8 carried both stx1 and stx2 genes. The eae and the enterohaemolysin (Ehly) gene sequences occurred at high frequencies in these STEC strains (41.6 and 50.0%, respectively). A total of 16 serotypes were identified. The serotypes O111:NM (four isolates), O111:H8 (two) and O118:H16 (one), currently described as enterohaemorrhagic E. coli (EHEC), were isolated from cattle in Brazil for the first time. These findings reinforce the importance of cattle as a reservoir of EHEC strains in Brazil.