Phenotypic and genotypic characterization of antimicrobial resistance in commonly isolated Salmonella serovars from chickens

Salmonellosis caused by Salmonella agents is the second most common zoonotic infection in humans. In recent years, Salmonella's increasing antimicrobial resistance (AMR) has been a concern. The major transmission route of Salmonella is consumption of contaminated poultry products. Therefore, monitoring of antimicrobial resistance in chicken-originated Salmonella is critically important. This study investigated AMR in four commonly isolated Salmonella serovars from chickens, namely Salmonella Enteritidis (S. Enteritidis), Salmonella Infantis (S. Infantis), Salmonella Kentucky (S. Kentucky), and Salmonella Typhimurium (S. Typhimurium). A total of 133 isolates were examined by phenotypic and genotypic AMR characterization. Resistance to 14 different antimicrobials and eight resistance genes were investigated in all isolates. The AMR test indicated that there was no resistant isolate to all antimicrobials while 14.3% were susceptible to all antimicrobials. The highest resistance was to sulfonamides (57.1%), nalidixic acid (48.1%), and tetracycline (39.1%). The highest susceptibilities were to cefotaxime (86.5%), cefoxitin (92.5%), ceftazidime (78.2%), and ceftriaxone (97%). S. Infantis and S. Kentucky isolates had higher resistance to all antimicrobials than S. Enteritidis and S. Typhimurium isolates. Significantly high multidrug-resistance (MDR) was detected in 50.4% of all isolates, although MDR prevalence varied widely between serovars: 78.7% of all S. Infantis isolates were MDR whereas only 18.8% of S. Enteritidis isolates were MDR. The most prevalent resistance genes were tetA (35.2%) and sul1 (31.6%), with 12.5% and 3.1% of S. Enteritidis isolates being positive for tetA and sul1, respectively, whereas 17.4% and 8.7% of S. Typhimurium isolates were positive. These rather low prevalence rates are probably due to effective monitoring of these serovars by control programs in Turkiye. The nondetection of mcr1 and mcr2 can be explained by the rare use of colistin in chicken flocks in Turkiye. The obtained findings emphasize the importance of AMR monitoring for Salmonella and the risks of chicken-originated isolates to humans.