Identification, Drug-resistance Analysis And Molecular Typing Of Salmonella Spp. Isolated From The Pork Production Chain

Salmonella is an important cause of food-borne illness in humans and widely distributed in word. Farm animals and foods of animal origin form an important source of human Salmonella infections. Although eggs (or products there of) and poultry meat are the biggest contributors to these outbreaks, pig meat has also been recognised as an important source of human salmonellosis since the early90s of last centary. This study aims to survey the distribution, antimicrobial susceptibility profiles and serotype of Salmonella in the pork production chain, and perform molecular typing in these isolates, in order to understand the relationship between strains from different sources in pork production chain.Slaughtering pigs and environment samples were collected from3slaughterhouses in Yangzhou, while1376pieces of pork were sampled in four cities of Jiangsu province, from2011to2012. Salmonella postive rate in slaughtering pigs and environent samples was46.6%and48.8%, respectively, however the positive rate only14.1%in pork. By statistical analysis, the prevalence of Salmonella in slaughterhouse were greater affected by seasonal factors and reached the peak in summer. Among Salmonella serovars identified, Salmonella Derby was most prevalent in pork and slaughterhouses, other serovars like Salmonella Typhimurium, Salmonella Meleagridis and Salmonella Anatum were also widespread. By incorporating predictive-modeling, floor contamination was the key factor in Salmonella contamination of the carcass surface. Antimicrobial sensitivity testing revealed that82.6%of isolates from pork and64.6%and74.5%of isolates from slaughtering pigs and environment were resistant to at least one antimicrobial. The highest rate of resistance was to tetracycline, which was66.3%and55.7%in pork and slaughterhouse, respectively. In additon, the resistance rates of ampicillin, streptomycin and sulfamethoxazole are also high. Though different sources, Salmonella Derby, Salmonella Typhimurium, Salmonella Meleagridis and Salmonella Anatum have shown a higher multiple drug resistance rates.58.3%of Salmonella Typhimurium isolated from pork resistant to4-6drug and16.7%of Salmonella Typhimurium isolated from pork resistant to7-9drug, which were both higher than other serotypes (P<0.05). In particular, one strain of Salmonella typhimurium found from slaughterhouse was resistant to11kinds of antibiotics. In pork and slaughterhouse, the most common drug-resistant and multi-drug resistance are TET and SXT TET, showing drug-resistant Salmonella spread between pork and slaughterhouse.Multilocus sequence typing (MLST) analysis demonstrated14and16sequence type (ST) patterns in pork and slaughterhouse, and ST40was the most common ST in different sources. Moreover, ST34and ST19were both found in pork and slaughterhouse. Clustering analysis showed that ST34and ST19belong to clone complex19(CC-19), which associated with human clinical salmonellosis.56isolates of Salmonella Derby and16strains of Salmonella Typhimurium were characterized by the technique of pulsed-field gel electrophoresis (PFGE) using the restriction enzyme Xba I.35and11PFGE patterns were generated among the selected isolates, respectively.4isolates of Salmonella Derby isolates with the same pattern (PF26) were isolated from cooling water, evisceration and carcass, suggesting that these four strains are belong to same Salmonella clone and occurred horizontal transmission along the production chain.The same PFGE pattern of Salmonella were both found in sample from carcasses in slaughterhouse and Yangzhou market pork, proving Salmonella spreading between the slaughterhouse and pork market. By PFGE type comparison, it was found Salmonella in pork at Yangzhou market was most correlated with Salmonella in C slaughterhouse.