[Antimicrobial resistance analysis and mechanism of Salmonella recovered from retail chicken carcasses in Beijing in summer, 2013].

OBJECTIVE: Research were carried out to determine the antimicrobial resistance and mechanism of Salmonella isolates recovered from retail chicken carcasses in Beijing in summer, 2013. METHODS: Broth microdilution method were used for antimicrobial susceptibility testing to obtain the minimal inhibitory concentration( MICs)against 11 antimicrobial compounds which belongs to 8 categories and 166 Salmonella strains isolated from 33 retail chicken carcasses in Beijing in summer, 2013 were tested. Cephalosporin resistant isolates were evaluated by ESBLs confirmation test, also resistance mechanism analysis was subjected to ciprofloxacin and cefotaxime co-resistant Salmonella isolates. RESULTS: 94. 6% isolates were resistant to at least one antimicrobial and 58. 4% were identified as multi-drug resistant strains. The highest rate of resistance was 92. 2% against nalidixic acid, followed by ampicillin( 48. 8%), ampicillin-sulbactam( 44. 0%), tetracycline( 44. 0%). There were 27 antimicrobial resistance spectrums with NAL and NAL-AMP-SAM being dominant spectrums. Totally, 41 ESBLs positive strains which contained 38 ciprofloxacin resistant isolates were recovered from 47 cefotaxime resistant strains. Detection of quinolones and β-lactams resistant genes for 38 ciprofloxacin and cefotaxime co-resistant and ESBLs positive Salmonella isolates indicate that QRDRs/PMQR/ESBLs antimicrobial resistance mechanism existed in these strains. Point mutations in gyrA and parC were identified in 37 isolates, and 38 isolates tested all contained PMQR genes such as qnrB、qnrS、oqxAB and aac( 6 ')-Ib-cr genes with a few mutations, while CTX-M( n = 35), TEM( n = 20), OXA( n = 36) type β-lactamases were detected. CONCLUSION: High level antimicrobial resistance and complicated mechanism existed among Salmonella recovered from retail chicken carcasses in Beijing in summer, 2013. In order to protect public health, tendency and further mechanism on antimicrobial resistance and transmissibility should be described deeply by on-going surveillance and research, while rational drug use regulatory managements should be carried out in the overall process of chicken production, slaughtering, transportation and marketing, as well as clinical treatment for human Salmonella infections.