| Salmonella is one of the important foodborne pathogens,which can cause the outbreak of salmonellosis worldwide.Studies have reported that Salmonella infections account for 30 to 90 percent of all food poisoning incidents caused by bacteria.Eating contaminated meat,eggs,vegetables and other foods are the main causes of Salmonella infection.Pork and chicken are important sources of consuming meat.China is a major producer and consumer of pork and chicken,once they are contaminated by Salmonella,it will not only threaten human health but also cause significant economic losses.Salmonella can live in the environment for a long time,so it is usually transmitted through the environment in the meat production chain,causing contamination of pork and chicken.At present,the contamination of Salmonella in meat products in a certain link of meat breeding,processing and marketing is investigated,and the data of comparative study on the whole production chain or multiple links in the production chain are less.The purpose of this study was to investigate Salmonella contamination in pork,chicken and its processing and marketing in some districts and counties of Chongqing,in order to find out the propagation law of Salmonella and provide solutions for the prevention and control of Salmonella contamination in animal food.Convenience sampling was carried out in pork,chicken and the environment in supermarkets and slaughterhouses from 12 districts of Chongqing,China.A total of 1112 samples were collected for isolation and identification of Salmonella,antimicrobial susceptibility testing,serotyping and multilocus sequence typing(MLST).115 Salmonella strains were isolated,with an isolation rate of 10.34%.The isolation rates of Salmonella in slaughterhouses and supermarkets showed no statistical difference(P>0.05).As for sampling sources,isolation rate of pork was significantly higher than that of chicken and environment(P<0.01).According to the types of environmental samples,only ground,cutting tools and table were found to harbor Salmonella in 9 kinds of environmental samples from slaughterhouses,with isolation rates of 33.33%,10% and 6.67%,respectively.While Salmonella was found in all 7 types of environmental samples from supermarkets.The antimicrobial-resistant phenotypes and gene types of 115 Salmonella strains were investigated.The results showed that the antimicrobial resistance rates of tetracycline,ampicillin and doxycycline were 73.04%,66.96% and 59.13%,respectively.50.43% Salmonella showed multidrug resistance(MDR),and the proportion of MDR strains in the total strains in supermarkets was significantly higher than that in slaughterhouses(P<0.05).The results of drug resistance gene test showed that the carrying rates of β-lactamase,tetracycline and sulfonamide resistance genes were higher than 70%.To explore the relationship between drug resistance gene and drug resistance phenotype,it was found that the strains carrying β-lactamase gene showed the highest percentage of drug resistance phenotype(87.80%).The proportion of positive sulfanilamide resistant strains showing related drug resistance phenotype was the lowest(53.19%).The serotype results showed that 30 serotypes were detected,with 25 in supermarkets and 10 in slaughterhouses.Derby(n=26),London(n=16),and Rissen(n=12)were the dominant serotypes.MLST divided the isolates into 23 types,including 20 from supermarkets and 8 from slaughterhouses.5 types were detected in both processes.There were 24,19 and 17 strains of Salmonella isolates identified as ST40,ST155 and ST469,respectively.Through combined analyzing the results of serotypes,STs and antimicrobial resistance spectrum,it was found that the environment of slaughterhouses in Qijiang,Yubei and Zhongxian had homology homologous Salmonella starins in pork,which indicating the existence of cross-contamination in slaughtering processes.In conclusion,in some districts and counties of Chongqing,pig and chicken products are contaminated to various degrees in the processing and marketing processes.Among them,the highest isolation rate of Salmonella is found in pork,with stronger crosscontamination.Therefore,environmental management in the slaughtering and marketing process of pork should be strengthened.Secondly,supermarkets,as a common part of meat sales,had more multi-drug resistant strains than slaughterhouses,and the sources of strains are more extensive.Once the infection occurs,the consequences are unimaginable.Therefore,attention should be paid to the health supervision of fresh food in supermarkets.This study also investigated the propagation of Salmonella in the meat production chain by combining serotyping and MLST.There was a correlation among MLST typing,serotyping and drug resistance.When the MLST data is gradually improved in the future,it can be combined with other typing methods,antimicrobial resistance,pathogenicity,etc.to enhance the accuracy of the results and reduce the workload. |
