| Salmonella is an important cause of food-borne illness that threatened livestock products and caused great threat to human health. Eggs and livestock products have been the major sources of food-borne illness, and the pork, the primary meat consumed in China, accounts for nearly 70 percent of animal proteins in Chinese diets, Therefore, great attention should be paid to reduce and control of Salmonella in pork during slaughter, processingof pigs. This study aims to survey the distribution, antimicrobial susceptibility profiles of Salmonella from a slaughterhouse and retail markets in Yangzhou area, meanwhile, the distribution of Salmonella spp. isolated from an animal hospital was also carried out to clarify the distribution, antimicrobial susceptibility profiles and serotypes of Salmonella in some areas of Yangzhou, it provide data for large-scale epidemiological survey and provide a scientific basis for the rational use of antibiotics and lay the foundation to the health of the pig industry in this area.1. Identification,drug-resistance analysis of Salmonella spp. isolated from a slaughterhouse, retail markets and an animal hospital in Yangzhou areaIn this study, we collect 1358 samples from Yangzhou slaughterhouse,182 samples from retail markets in Yangzhou area and 187 samples from the animal hospital of Yangzhou University between 2015 and 2016. Salmonella spp. from samples was isolated according to GB 4789.4-2010 and Salmonella virulence genes were detected from the isolates by polymerase chain reaction(PCR). Salmonella positive rate in the slaughterhouse samples and retail markets samples was 10.5% and 19.7%, respectively, however the positive rate only 2.6% in samples of the animal hospital. By statistical analysis, the prevalence of Salmonella in the slaughterhouse and retail markets was not varied with different seasons. Among Salmonella serovars determined, Salmonella Derby was most prevalent in the slaughterhouse, which rate was 63.6%, other serovars, like Salmonella Typhimurium and Salmonella Rissenwere also widespread. Salmonella Derby and Salmonella Rissen rate was 27.8%, which was the most common in Salmonella spp. isolated in retail markets, Salmonella Anatum took second. But all Salmonella strains from the animal hospitalwere classified as Salmonella Typhimurium. Antimicrobial resistance of all Salmonella isolates mentioned above was determined by antibiotic susceptibility test, the results showed that,85.2% of Salmonella isolates were resistant to tetracycline, in addition, the resistance rates of Doxycycline and Ampicillin were also high.57.4% of isolates from the slaughterhouse and 44.4% of isolates from retail markers were co-resistant to nine antimicrobials, and all the isolates from the animal hospital were resistant to nine antimicrobials.2.Virulence genes detection and PFGE typing analysis of Salmonella spp. isolated from the slaughterhouse,retail markets and the animal hospital,and the pathogenicity of Salmonella isolates in KM miceTo investigate the distribution of virulence genes of all Salmonella isolates, six virulence genes(mogA, sscA, sseC, mgtC, siiE, sopB) were selected to be detected by PCR, the virulence gene positive rates of all Salmonella strains were mogA 81.5%(150/184), sscA 70.1%(129/184), sseC 68.5%(126/184), mgtC 87.5%(161/171), siiE 85.7%(158/184), sopB 70.7%(130/184) respectively. There were 57 Salmonella strains which harbored all the virulence genes tested. Among them,47 Salmonella strains came from the slaughterhouse (82.5%),5 Salmonella strains originated from retail markets, and 5 Salmonella strains from the animal hospital (8.7% each).27 isolates of Salmonella Derby,9 strains of Salmonella Rissenand 17 strains of Salmonella Typhimurium were characterized by the pulsed-field gel electrophoresis (PFGE) using the restriction enzyme Xba I.18,8 and 17 PFGE patterns were generated among the selected isolates respectively. The same PFGE patterns of Salmonella were found in samples from both the slaughterhouse and retail markets, proving Salmonella spreading between the slaughterhouse and retail markets.Then selected 5 representative isolates and the reference strain Salmonella choleraesuisat a dose of 108 CFU were used to challenge 6-8 week old KM mice by intraperitoneal injection, most of the mice reached its death peak at 8-12 h post-challenge, all groups of mice were died within 24 h post-challenge. Postmortem of the dead mice showed acute septicemia of visceralorgans, and exudative inflammation. LD50 of JY-1 isolate was 1.48×105 and the mortality rate was 52.8%. The virulence of JY-1 isolate is highest among tested isolates, while the pathogenicity of T4-D1 isolate was equal to the reference strain CVCC503. |
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