Salmonella isolated from the slaughterhouses and correlation with pork contamination in free market

This study surveyed the distribution, antimicrobial susceptibility profiles and serotype of Salmonella isolated from three slaughterhouses, and performed molecular typing on these isolates, to understand the relationship between strains of Salmonella obtained from the pork production chain in Yangzhou, China. Samples from slaughtered pigs and the slaughtering environment were collected from three slaughterhouses in Yangzhou, Jiangsu province, from October 2012 to July 2013. The positive identification rates of Salmonella in slaughtered pigs and the environmental samples were 46.6% and 48.8%, respectively. The prevalence of Salmonella in slaughterhouses were affected by seasonal factors and reached the peak in summer. Among the Salmonella serovars identified, S. Derby was most prevalent in slaughterhouses, but other serovars like S. Typhimurium, S. Meleagridis and S. Anatum were also widespread. Antimicrobial susceptibility testing revealed that 32 and 131 different MDR patterns were found among the strains from the environment and slaughtered pig samples, respectively. Fifty-six isolates of S. Derby and 16 strains of S. Typhimurium were characterized by the technique of pulsed-field gel electrophoresis (PFGE) using the restriction enzyme Xba I. 35 and 11 PFGE patterns were generated among the selected isolates. Four isolates of S. Derby isolates with the same pattern (PF26) were isolated from cooling water, evisceration and carcass, suggesting that cross contamination occurred between the environment and the slaughtered pigs. Six S. Typhimurium in cluster 1 with the same ST type (ST19) came from different parts of the slaughtered pig, which could have occurred because of horizontal transmissions along the slaughtering process. The same PFGE patterns of Salmonella were found in both samples from carcasses in the slaughterhouse and in the Yangzhou pork market, proving that Salmonella had spread from the slaughterhouse to the pork market. In conclusion, our study demonstrate that serious cross contamination occurred in Yangzhou slaughterhouses and can contribute Salmonella contamination in pork sold in the local public market.