Objective: Antimicrobial susceptibility to quinolone and fluoroquinolones and the related genes of chickenborne Salmonella in Shaanxi, Henan, Sichuan and Beijing provinces were studied to better understand the development of antimicrobial resistance and routes of transmission to ensure food safety.
Methods: Antimicrobial susceptibility was tested according to agar dilution method. GyrA and parC gene mutations of quinolone resistance determination region (QRDR) of fluoroquinolone resistant Salmonella and the resistant genes of qnrA, qnrB, qnrS and aac (6')-Ib-cr were determined using PCR and DNA sequencing analysis.
Result: Among the 390 Salmonellae isolates, 63.59% were resistant to nalidixic acid, followed by ciprofloxacin (21.28%), levofloxacin (16.67%), and gatifloxacin (14.62%). Among 248 nalidixic acid resistant Salmonella, antimicrobial resistant genes carried by plasmid were detected as aac(6')-Ib-cr (20.16%), qnrA (10.89%), qnrB (10.08%) and qnrS (1.61%), respectively. In total 199 point mutations were detected in gyrA and parC of 83 fluoroquinolone-resistant Salmonella isolates. The most common mutations in gyrA gene was Ser83Phe and Asp87Gly double mutation, followed by Ser83Phe and Asp87Asn double mutation, Ser83Tyr, Ser83Phe, Asp87Gly. Sixty-five point mutations detected in parC was Ser80Arg.
Conclusion: Antimicrobial resistance of Salmonella recovered from chicken in the four provinces was common. Genetic elements including mutations of unwindase, topoisomerase, and plasmid with antimicrobial, played important roles in the antimicrobial resistance of Salmonella.