Prevalence Of Extended-spectrum Β-lactamases(ESBLs)-Producing Salmonella In Retail Raw Chicken Carcasses And Mechanism Of Antibiotic Resistance Mediated By Plasmid

β-Lactamases and extended-spectrumβ-lactamases（ESBLs）producing pathogenic bacteria including Escherichia coli and Klebsiella pneumoniae were widely studied previously in China,but seldom focused on foodborne Salmonella.This study aimed the prevalence of ESBLs producing Salmonella from retail raw chicken carcasses and plasmid-mediatedβ-lactams resistance horizontal transmission,for perfecting the information ofβ-lactamases producing Salmonella in China.A total of 890 Salmonella isolates that recovered from retail chicken carcasses collected from Shaanxi,Henan,Sichuan and Guangdong province were screened for ESBLs-producting ones via the double-disk synergy test and polymerase chain reaction.Tenβ-lactamases and ESBLs encoding genes including bla CMY-2,bla TEM-1,bla TEM-1b,bla TEM-116,bla OXA-1,bla PSE-1,bla CTX-M-3,bla CTX-M-55,bla CTX-M-22 and bla CTX-M-15were identified in the 96 ESBLs-producing Salmonella isolates.Of which,57.3%were detected harboring bla _TEM-1,followed by bla _OXA-1（30.2%）,bla _CTX-M-15（24.0%）,bla _CTX-M-3（18.8%）and bla _PSE-1（7.3%）.Significant differences of prevalence rates of ESBLs producing Salmonella were detected in different sample place,year,seasons,chicken types and Salmonella serovars,respectively（P<0.05）.Among 96 ESBLs producing Salmonella,88（91.7%）isolates harbored transposons ranged from 4.2%for Tn903 to 76.0%for Tn21 via PCR.A total of 59 PFGE profiles were detected in these 96 isolates after subjected to PFGE analysis.Sixty ESBLs producing salomella previously acquired in our lab combined 96 ESBLs producing ones of the current study,a collection oftotally 156 ESBLs producing Salmonella were identified for 29virulence genes.Twenty nine virulence genes were detected ranging from 0%for rck to 90.6%for mar T and ste B genes.Redundancy analysis biplot results indicated that the distributions of virulence genes were highly significantly influenced by sampling location（P<0.01）,especially for sod C1 and pip D.Twenty six isolates harbored bla _CTX-M-3were selected for conjugation test.Thirteen（50.0%）transconjugants were acquired.The minimum inhibitory concentrations（MICs）of antibiotics to most transconjugants were significantly higher than those recipients and corresponding donor,especially the MIC of cephalosporin to the transconjugants.S1-PFGE and Southern-blot were used for bla _CTX-M-3location determination on plasmid.The results indicated that bla _CTX-M-3located on larger plasmid,which was about215～400kb in size.In conclusion,ESBLs were widly prevalent in Salmonella from retail chicken carcasses in China,and the antibiotic resistance could be transmitted via horizontal genes transfer,which should prompt us to establish necessary surveillance system for the transmission.