| Salmonella is one of the most common foodbome disease caused human food poisoning, and fevers, gastroenteritis, sepsis caused by Salmonella are the most common. In recently years, the incidence of resistance to antimicrobials among Salmonella has been steadily rising, and resistance may transimit to human via food chain. The prevalence and transmition of Salmonella, especially resistant Salmonella among food chain poses a significant threat to public health. In our study, we collected 189 Salmonella strains from broiler slaughter processing in Sichuan province and did the thorough research about serotype analysis, drug resistant analysis, class 1 integrons/gene cassettes, mutations in gyrA and parC gene, sulfanilamide resistant gene (sul1, sul2 and sul3 gene), tetracycline resistant gene (tet(A), tet(B), tet(C) and tet(G) gene), beta-lactam resistant gene (blaTEM, blaCTX-M and blaSHV gene), aminoglycosides resistant gene (aac(3)-Ⅱ, aac(3)-Ⅳ and ant(2’)-Ⅰ gene), florfenicol resistant gene and pulsed-field gel electrophoresis (PFGE) typing analysis on the basic of identification.1 Isolation and identification of Salmonella isolates from broiler slaughter processing627 samples of cecum (pre-slaughter), carcass surfaces, after chilling and end production in 2012 to 2014. Salmonella isolates were performed according to GB 4789.4-2010 and further identified by special virulence genes (invA and hut gene) of Salmonella. The results were as follows. A total of 189 Salmonella isolates were detected from broiler slaughter processing, containing 132 S. Enteritidis,29 S. Typhimurium and 28 untyped Salmonella. The prevalence of Salmonella was 30.1% among broiler slaughter processing, and 69.8% of isolates was S. Enteritidis. The prevalence of Salmonella among cecum, carcass surfaces, after chilling and end production was 47.96%,18.78%,31.33% and 14.00%, respectively.2 Analysis of antibiotic resistance of Salmonella isolates from slaughter processingAll the 189 Salmonella isolates were tested against 10 different antimicrobial agents in accordance with the standard Kirby-Bauer disk diffusion method of the Clinical and Laboratory Standards Institute (CLSI,2015).99.5%(n=188) of the 189 Salmonella strains were resistant to nalidixic acid,87.8% were resistant toampicillin,48.7% to ciprofloxacin,51.9% to tetracycline,48.1% to trimethoprim-sulfamethoxazole,34.4% to spectinomycin, and low resistance to fluorine benzene, gentamycin, amoxicillin-clavulanic acid and ceftriaxone.60.8% of isolates showed multi-drug resistance and 49 kinds of resistance patterns were found. Multi-drug resistance was much more serious along slaughter processing ranging from 50.0% to 78.6%.3 The prevalence of resistant gene among resistant Salmonella3.1 The prevalence of class 1 integrons/gene cassettes among multi-drug resistant isolates Among 115 multi-drug resistant strains, the intI1 gene was present in 37.4%(n43) isolates.72.4%%(n=21) of S. Typhimurium harbored the intI1 gene, comparing with 31.7%(n=19) of S. Enteritidis. Likewise, the higher frequency of intll gene was found from freezing meat samples (72.7%; n=8), compared with 38.9%(n=7),34.5%(n=19) and 29.0%(n=9) of isolates from carcass surfaces, feces, and chilling meat samples, respectively. Among the 43 intI1-positive isolates, 21 isolates harbored the different size segments of gene cassettes. The blaoxA30-aadA1 and dfrA1-orfC gene cassette were found.3.2 Mutations in gyrA and parC geneMAMA PCR was used to detected mutations at Asp87 and Ser83 in gyrA gene and Ser80 and Glu84 in parC gene among quinolone resistant Salmonella. The prevalence of mutations at Asp87 and Ser83 in gyrA gene was 80.5% and 75.0%, respectively, and the occurrence of mutations at Ser80 and Glu84 in parC gene was 72.9% and 76.6%, respectively.3.3 The prevalence of beta-lactam resistant genePCR was used to detect blaTEM, blaSHV, and blaCTX-M gene among 166 beta-lactam resistant Salmonella. The blaTEM gene (93.4%;n=155)was most prevalent in β-lactam resistant isolates, followed by blaCTX-M gene (12.7%; n=21) and the blaSHV gene was not detected in any of the isolates.3.4 The prevalence of aminoglycosides resistant genePCR was used to detect aac(3)-Ⅱ, aac(3)-Ⅳ and ant(2’)-Ⅰ gene among 79 aminoglycosides resistant Salmonella. Among 79 aminoglycosides resistant strains, the prevalence of aac(3)-Ⅱ and aac(3)-IV gene was 35.4% and 53.2%, respectively, and none of strains harbored ant(2’)-I gene.3.5 The prevalence of sulfonamides resistant genePCR was used to detect sull, sul2 and sul3 gene among 91 sulfonamides resistant strains. Among 91 sulfonamides resistant strains, the prevalence of sull, sul2 and sul3 gene was 50.5%,97.8%, and 50.5%.3.6 The prevalence of tetracycline resistant genePCR was used to detect tet(A), tet(B), tet(C) and tet(G) gene among 98 tetracycline resistant strains. Among 98 tetracycline resistant strains, the prevalence of tet(A), tet(B) and tet(C) genes was 25.5%,50.0% and 71.4%, respectively and none of strains carried tet(G) gene.3.7 The prevalence of florfenicol resistant genePCR was used to detect floR gene among florfenicol resistant strains. Among 45 florfenicol resistant strains,44 (97.8%) of isolates carried floR gene.3.8 The PFGE typing of Salmonella isolates from broiler slaughter processingAfter digestion by X-bal, PFGE was used to assess the genetic relatedness of 189 Salmonella isolates from broiler slaughter processing. PFGE fingerprinting profiles showed the similarity amongl89 Salmonella strains was from 27.25%～100% and 21 PFGE types were found. Isolates belonging to the same serovar clustered together. The study indicated that Salmonella may transmit from live chicken to end production via slaughter chain and cross-contamination between circumstance and human was existed in all slaughtering.This study analysed the pollution and antibiotic resistance of Salmonella along broiler slaughter processing, which provided the basic data for the monitoring of Salmonella contamination and resistance. We also detected the resistant gene of Salmonella, which laid the foundation for the mechanisms of resistance among Salmonella. Finally, PFGE was used to assess the genetic relatedness of Salmonella isolates from broiler slaughter processing and provided the theoretical and practical basis for Salmonella spread. |
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