Antibiotic Resistance Patterns and Detection ofblaDHA-1inSalmonellaSpecies Isolates from Chicken Farms in South Korea

Fifteen nonrepetitive ampicillin-resistantSalmonella spp. were identified among 91Salmonella sp. isolates during nationwide surveillance ofSalmonella in waste from 131 chicken farms during 2006 and 2007. Additional phenotyping and genetic characterization of these 15 isolates by using indicator cephalosporins demonstrated that resistance to ampicillin and reduced susceptibility to cefoxitin in three isolates was caused by TEM-1 and DHA-1 β-lactamases. Plasmid profiling and Southern blot analysis of these three DHA-1-positiveSalmonella serovar Indiana isolates and previously reported unrelated clinical isolates of DHA-1-positiveSalmonella serovar Montevideo,Klebsiella pneumoniae , andEscherichia coli from humans and swine indicated the involvement of the large-size plasmid. Restriction enzyme digestion of the plasmids from the transconjugants showed variable restriction patterns except for the twoS almonella serovar Indiana isolates identified in this study. To the best of our knowledge, this is the first report of the presence of the DHA-1 gene amongSalmonella spp. of animal origin.