| Salmonella, one of the most important zoonotic pathogens, is harmful to pig industry development and animal derived food hygiene problem. Salmonella can be carried by both healthy pigs, and sub-healthy pigs, which brought a huge risk to the same group, and healthy pig farm. Up to now, there are only few reports on the healthy pigs carried Salmonella in China. This study aims to investigate the prevalence, serovars and antimicrobial resistance of Salmonella spp. in scale pig farms from Jiangsu Province. All Salmonella isolates were characterized using different molecular subtyping methods, such as multilocus sequence typing (MLST) and pulsed-field gel electrophoresis (PFGE). It could be very useful to find key link in the process of Salmonella contamination and to provide data for the control of Salmonella. 1. Identification, drug-resistance analysis of Salmonella spp. isolated from the scale pig farms in Jiangsu ProvinceA total of 1470 samples were collected from the seven scale pig farms (A, B, C, D, F, E, G) in six cities of Jiangsu Province from 2014 to 2015. The positive rate of Salmonella spp. was 15.9%(233/1470), and it was different in every farm. Statistical analysis showed that the nursery is critical point of Salmonella contamination in farm A, but fattening is critical one in farm B. Identification of Salmonella serovars showed that the most dominant serotype was Salmonella Typhimurium, followed by Salmonella Derby which was the most widespread serotype in the farms. Antimicrobial sensitivity test indicated that the highest resistance was to tetracycline (68.3%). Resistance to other antimicrobial agents such as ampicillin, streptomycin, nalidixic acid, cefazolin and trimethoprim-sulfamethoxazole were also common. In p-lactam antibiotics resistance cephalosporin antibiotics cefazolin significantly higher than penicillin antibiotics amoxicillin (P< 0.01). In the aminoglycoside antibiotics streptomycin resistance significantly higher than the other three kinds of antibiotics (P< 0.01). The same case was observed for resistance to NAL and other antimicrobial agents belonging to the quinolone and fluoroquinolone families (P< 0.01). Multidrug resistance was frequently observed in S. Typhimurium, S. London and S. Derby, among which S. Typhimurium was most prominent (92.4%), S. Typhimurium isolates resistance to nine or more antibiotic drug resistance reached 72.2%.2. Molecular subtyping of Salmonella spp. isolated from the scale pig farms in Jiangsu ProvinceA total of 10 sequence types (STs) were identified among the Salmonella isolates from the different source. ST19 was the main ST and ST40 was the most prevalent ST in all of the sources, which indicated that ST description is relatively stable from swine farms in Jiangsu province.50 isolates of Salmonella Typhimurium and 38 strains of Salmonella Derby were characterized by PFGE using the restriction enzyme Xba I.40 and 22 PFGE patterns were generated among the selected isolates, respectively. Among the isolates from the first farm A, PFGE patterns of S. Typhimurium A1-B2 and A1-Y8 from nursery and finishing were found respectively to have the identical pulsotype, demonstrated that these three strains may belong to the same clone and it maybe caused by horizontal transmission of the strain along with the production line and spread caused serious cross-contamination. Production processes for different batches of different portions of S. Typhimurium PFGE type converge Al-G1, Al-Y1 and A2-B2, indicated that the isolates were the resident microflora in the site, and could cause persistent pollution. The different PFGE fingerprint profiles were found in S. Derby and it may be because of the source of pigs, management mode and breeding environment in every farm. The high similarity cluster evolution and strips was found from farm A and farm C shows that S. Derby may have a very a close relationship of the genetic evolution between farm A and C. |
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