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The main purpose of this study was to determine the prevalence of Escherichia coli 0157 on bovine carcasses before and after chilling at a large slaughterhouse located in the city of Barcelona, Spain, to assess the effectiveness of dry chilling on reducing E. coli 0157 contamination of carcasses. In addition, the study characterized the E. coli 0157 strains isolated in terms of virulence factors, antibiotic susceptibility, and their genetic diversity. Individual bovine carcasses were sampled before (n = 300) and after (n = 300) chilling over an 8-month period. Positive samples for E. coli 0157 were subjected to virulence screening by PCR (stxi, stx2, and eaeA genes and thsfliCm gene), antimicrobial susceptibility testing, and molecular typing by pulsed-field gel electrophoresis. A total of 9.7% (29 of 300) of the nonrefrigerated carcasses examined and 2.3% (7 of 300) of the refrigerated carcasses were positive for E. coli 0157. All the isolates were serotype 0157:H7, 92% (33 of 36) carried the stxu stx2, and eaeA genes, and 8% (3 of 36) carried the stx2 and eaeA genes. Antimicrobial susceptibility testing showed a high degree of resistance: 29 strains (81%) were resistant to at least 1 antimicrobial of the 12 antimicrobials tested; 69% (25 of 36) were resistant to 4 or more antimicrobials. Molecular typing by pulsed-field gel electrophoresis found a high diversity of genetic types, implying little cross-contamination in the slaughterhouse. This study confirms that E. coli 0157:H7 is present on the carcasses slaughtered in Spain, although its prevalence is reduced by the dry chilling process used. The recovered isolates showed potential pathogenesis and a high degree of multidrug resistance, confirming the importance of bovine meat monitoring. [ABSTRACT FROM AUTHOR]