Molecular characteristics of antimicrobial resistance determinants and integrons in Salmonella isolated from chicken meat in Korea

The increase and spread of antimicrobial resistance, particularly multidrug resistance (MDR), in Salmonella isolated from food animal pose a serious public health concern worldwide. Therefore, the objective of this study was to characterize antimicrobial resistance and analyze the transferability of integrons and antimicrobial resistance genes in MDR Salmonella isolates from retail chicken meat in Korea. Among the 57 Salmonella isolates, 43 (75.4%) showed resistance to at least 1 antimicrobial agent and 29 (50.9%) exhibited MDR. The highest resistance was to nalidixic acid (73.7%), ampicillin (50.9%), tetracycline (42.1%), chloramphenicol (33.3%), and trimethoprim/sulfamethoxazole (33.3%). beta-lactamase-encoding genes were detected in 9 (31.0%) of 29 beta-lactam-resistant isolates. These genes were as follows: bla(CMY-2) (1 S. Albany), bla(CTX-M-79) (1 S. Virchow), and bla(CTX-M-15) (6 S. Virchow and 1 S. Enteritidis). Seventeen (70.8%) of the 24 tetracycline-resistant isolates harbored only tetA. Among the 19 trimethoprim/sulfamethoxazole-resistant isolates, sul1 was only identified in 3 (68.4%) isolates. cmlA was detected in 4 (21.1%) of the 19 chloramphenicol-resistant isolates. Both aminoglycoside-resistant isolates were positive for ant(2 '')-I. Class 1 integrons were observed in 28 (49.1%) isolates belonging to S. Albany (21 isolates), S. Virchow (6 isolate), and S. Enteritidis (1 isolate). All 29 MDR isolates carried one or more integrons and antimicrobial resistance genes. All isolates harboring the ESBL and pAmpC genes exhibited resistance to at least 4 different classes of antimicrobials, including cephalosporins and noncephalosporins. Furthermore, most (79.3%) of the MDR isolates carried 1 or 2 of conjugable plasmids, and the transfer of integrons and resistance genes via plasmids was confirmed in transconjugants, which showed resistance patterns similar to those of the donor strains.