Animal and human multidrug-resistant, cephalosporin-resistant Salmonella isolates expressing a plasmid-mediated CMY-2 AmpC beta-lactamase

Salmonella spp. are important food-borne pathogens that are demonstrating i ncreasing antimicrobial resistance rates in isolates obtained from food ani mals and humans. In this study, 10 multidrug-resistant, cephalosporin-resis tant Salmonella isolates from bovine, porcine, and human sources from a sin gle geographic region were identified. All isolates demonstrated resistance to cephamycins and extended-spectrum cephalosporins as well as tetracyclin e, chloramphenicol, streptomycin, and sulfisoxazole. Molecular epidemiologi cal analyses revealed eight distinct chromosomal DNA patterns, suggesting t hat clonal spread could not entirely explain the distribution of this antim icrobial resistance phenotype. However, all isolates encoded an AmpC-like b eta-lactamase, CMY-2. Eight isolates contained a large nonconjugative plasm id that could transform Escherichia coli. Transformants coexpressed cephalo sporin, tetracycline, chloramphenicol, streptomycin, and sulfisoxazole resi stances. Plasmid DNA revealed highly related restriction fragments though p lasmids appeared to have undergone some evolution over time. Multidrug-resi stant, cephalosporin-resistant Salmonella spp. present significant therapeu tic problems in animal and human health care and raise further questions ab out the association between antimicrobial resistance, antibiotic use in ani mals, and transfer of multidrug-resistant Salmonella spp. between animals a nd man.