Prevalence and Characterization of Salmonella in Three Typical Commercial Pig Abattoirs in Wuhan, China

This study was designed to investigate the prevalence and characteristics of Salmonella in three Chinese pig abattoirs (A, B, and C) in Wuhan city in 2016. Four types of pig samples were collected and cultured for Salmonella. Salmonella was detected from 329 samples among the 1440 tested (22.9%). There was no significant difference in the overall prevalence between the first visit and the second visit and among the three abattoirs. Rectal swabs (RS) exhibited a significantly higher prevalence than carcass swabs and pork. A total of 177 isolates were characterized by multilocus sequence typing, serotyping, and antimicrobial susceptibility testing. Among 17 sequence types (STs) and 13 serotypes detected, ST40, ST469, and ST34, corresponding to serovars Derby, Rissen, and Typhimurium, respectively, were predominant. The isolates from different abattoirs exhibited diverse ST distribution. The minimum inhibitory concentrations were determined using the microdilution broth method. Resistance to at least one of the antimicrobials was observed for 96.6% of the strains (171/177), and multidrug resistant (MDR) isolates accounted for 75.7% of the strains (134/177). The highest resistance proportion was for tetracycline (92.7%), and the lowest was for cefotaxime (14.1%). The isolates from abattoir A exhibited a significantly lower MDR proportion than those from other abattoirs (p < 0.05). The isolates recovered from RS and pork samples exhibited significantly higher MDR proportions than those recovered from carcass swab samples. Notably, among three predominant STs of isolates, the ST34 isolates showed the highest MDR proportion. In view of the high Salmonella prevalence and antimicrobial resistance, great attention must be paid to the monitoring and controlling of Salmonella in a full pork production chain.