Antimicrobial resistance genes in Salmonella enterica isolates from poultry and swine in Thailand.

A total of 184 resistant Salmonella enterica isolated from poultry and swine were investigated for the distribution of and associations between various antimicrobial resistance genes. All the isolates were screened for the presence of class 2 and 3 integrase genes and 18 resistance genes corresponding to their resistance phenotypes. None of the isolates carried class 2 and 3 integrons. The investigated resistance genes were responsible for resistance in 78% of the isolates. All the strains harboring more than one resistance gene were resistant to three or more antimicrobials. The bla(TEM), cmlA, tetA, dfrA12, sul3, aadA1 genes were detected in the majority of strains resistant to ampicillin (87%), chloramphenicol (63%), tetracycline (60%), trimethoprim (42%), sulphonamides (42%) and streptomycin/spectinomycin (61%), respectively. Two ciprofloxacin-resistant isolates had a single point mutation leading to Ser-83-Phe in GyrA or Thr-57-Ser in ParC. Statistical analysis revealed good correlation between the presence of antimicrobial resistance genes and corresponding resistance phenotype (p<0.01). The results indicated that the resistance genes play a major role in conferring resistance among the Salmonella isolates investigated.