Isolation, Identification, Antibiotic Resistance Analysis And Pulsed-field Gel Electrophoresis Genotyping Of Salmonella From Main Meat Production Chain In Sichuan

Salmonella is one of important pathogenic bacteria threatened livestock products in enterobacteriaceae, and the WHO has listed it as a serious hazard and moderate hazard of food-borne pathogens. Animals before their death and the subsequent slaughter and processing, transportation, storage and sales aspects are easy to produce and spread the salmonella. Extensive use of antibiotics in livestock and poultry raising make animal food easily become a "reservoir" of drug-resistant bacteria. Researches showed that salmonella their resistance to antibiotics had been in the steady growth and the resistance may be transferred to the pathogenic bacteria or probiotics of human through the food chain. Therefore, doing some research about distribution and spread of salmonella, especially drug-resistant salmonella in meat production chain is significant for ensuring food safety and public health. In this study, we collected165strains of salmonella from large-scale farms, downstream slaughterhouse and meat market in some key areas of Sichuan province and did the thorough research about serotype analysis, drug-resistance analysis, and pulsed-field gel electrophoresis (PFGE) typing analysis on the basic of identification.1. Isolation and identification of salmonella in the meat production chain1382samples of adult poultry feces or raw meat were collected from pork, chicken, duck production chain (farms-slaughterhouse-sales market) in2010and2011. The suspected salmonella were gained by using CHROMagar. All suspected salmonella were identified by using invA and hut genes duplex PCR amplification method, and then the positive strains were used for serotype analysis. Results:A total of165samples were detected Salmonella, the contamination rate was11.94%(165/1382); the Salmonella contamination rate of the production chains (pork, chicken, duck) were13.51%(112/829),6.94%(30/432),19.01%(23/121), respectively;165strains of salmonella were detected in14serotypes and most of them were S. derby, S.typhimurium, S.potsdam, S.give, the respective proportions of46.06%,9.70%,5.45%,3.64%.It was serious that pollution of Salmonella in Sichuan main meat production chain,it was showed that Salmonella of advantage serotype horizontal transmission in pork production chain, exogenous pollution of the chicken and duck production chain downstream was serious. 2. Analysis of Antibiotic Resistance of Salmonella in the meat production chain According to the broth microdilution method recommended by the WHO, the drug sensitivity of the165strains of salmonella was tested by using the10kinds of antibiotics (combination). The susceptibility results were determined by CLSI standards (2010). Results:in the pork production chain, the highest drug-resistance of all strains was tetracycline (89.29%), the higher drug-resistance were spectinomycin, trimethoprim/sul-famethoxazole, nalidixic acid and ampicillin, no drug-resistance was cephalosporins ceftiofur, multiple drug-resistance rate was48.21%, a total of19kinds of resistance patterns,most of drug resistance rates of strains from upstream to downstream were decline: in the chicken, the higher drug-resistance were spectinomycin, tetracycline, nalidixic acid, trimethoprim/sulfamethoxazole, the rates were all above45%, multiple drug-resistance rate was66.67%, a total of19kinds of resistance patterns; in the duck production chain, the higher drug-resistance were trimethoprim/sulfamethoxazole, nalidixic acid, tetracycline, spectinomycin and ampicillin, the rates were73.91%,69.57%,52.17%,39.13%and34.78%, the drug-resistance of ciprofloxacin, amoxicillin/clavulanic acid, ceftiofur, florfenicol and gentamicin were lower, the rates were all below20%, and multiple drug-resistance rate was73.91%, a total of14kinds of resistance patterns, most of drug resistance rates of strains from upstream to downstream went up.3. PFGE typing analysis of Salmonella The strains of salmonella were selected through different sources of strains, serotypes and resistance patterns; with reference of the United States the CDC criteria for PFGE typing. Results:the PFGE genotypes of the97strains of salmonella the similarity was from40%to100%; there were34PFGE spectral pattern from the pork production chain of74strains of salmonella, it was existing the phenomenon of salmonella along the production chain horizontal spread;12PFGE spectral pattern from the chicken production chain of15strains of salmonella,and7PFGE spectral pattern from the duck production chain of8strains of salmonella, both of their PFGE spectral pattern were complex,but duck production chain was existing the phenomenon of salmonella along the production chain horizontal spread.This study analysed the pollution and the resistance of Salmonella in main meat production chain, it provided the basic data for the monitoring of Salmonella contamination and resistance. PFGE typing of Salmonella in meat production chain laid the foundation for the study of the mechanisms for the dissemination of Salmonella in the food chain.The findings of this paper has certain theory significance and the pratical value.