Dissemination amongst humans and food products of animal origin of a Salmonella typhimurium clone expressing an integron-borne OXA-30 beta-lactamase.

OBJECTIVES Characterization of the molecular basis for beta-lactam resistance and evaluation of the clonal relatedness among nine isolates of multidrug-resistant Salmonella typhimurium recovered from seven clinical human samples and two pork end products. METHODS The isolates were examined for susceptibility to antimicrobial agents. The relationships between resistance genes, class 1 integrons, plasmids and isolates were screened by molecular methods such as polymerase chain reaction and restriction fragment length analysis. RESULTS A bla(OXA-30) gene, located in a class 1 integron, was detected in all isolates. This integron was present on a conjugative plasmid in all but one isolate. By pulsed-field gel electrophoresis, it was determined that all strains share the same chromosomal type. CONCLUSIONS This study demonstrates the spread of an OXA-30-producing S. typhimurium in Portugal, suggesting dissemination of a resistant clone through the food chain.