Isolation And Identification Of Salmonella Strains From Swine In Some Areas Of Jiangsu Province And Study On Their Some Biological Characteristics

Salmonella can widely infect with a variety of animals including people with important significance in public health of human and animal disease now. Human beings may infect Salmonella through the food contaminated by Salmonella. Salmonella has repeatedly caused major food poisoning at home and abroad. In China, pork consumption ranks first in the consumption of meat. Therefore, study of swine Salmonella has very important significance for the pig industry and food safety. The aim of this study is to survey carrier and virulence conditions of swine Salmonella in some parts of Jiangsu Province and provide data for large-scale epidemiological survey in this area.In this study, we collect 527 samples from Yangzhou slaughterhouse and animal hospital of Yangzhou University in total in the year of 2014, and 42 strains were isolated. Biochemical experiments showed that all the isolates were characteristic of Salmonella, but the majority of the isolates (24/42) utilized malonate, which was inconsistent with the typical biochemical reaction of Salmonella, and a few isolates did not produce hydrogen sulfide, together with those being negative in lysine decarboxylase test, isolates with the typical biochemical reaction of Salmonella accounted for only 19.05%(8/42), which show the differences in the biochemical characteristics between strains isolated in this study and typical ones.With the serotype identification of all the isolates, a total of 28 isolates was determined, of which the first place is Salmonella Lexington isolates (52.38%) whose antigen formula is 10:Z10:1,5, the second is isolates with 02 serotype,10 isolates (23.81%), the remaining serotype isolates included one or two strains for each O serotype. Of all the isolates originated in this study, only Salmonella typhimurium is known to be pathogenic to pigs up to now, the remaining isolates in general are known to be non-pathogenic to pigs while are able to persist in healthy pigs, some strains can cause disease in other hosts. In this study, we chose 20 kinds of antibiotics including carbenicillin, amoxicillin, cefazolin, cefotaxime, furazolidone, kanamycin, gentamicin, streptomycin, amikacin, tetracycline, sulfamethoxazole, ciprofloxacin, enrofloxacin, nalidixic acid, chloramphenicol, polymyxin B, florfenicol, ampicillin, cefalexin, levofloxacin to carry out drug susceptibility test. The results showed that more than 50% of isolates were resistant to 14 antibiotics, the resistance rate of isolates to ampicillin reached 100%, and the resistant rate to both tetracycline and sulfamethoxazole was more than 90%. Beside these, the majority of isolates (39/42) also showed multiple drug resistance. Isolates with resistance to 13 out of 20 drugs accounted for 52.38% (22/42), those with resistance to 10 or more drugs is 73.81%(31/42).Based on the polymerase chain reaction (PCR) analysis of core protein gene of pathogenicity island and pulse field gel electrophoresis (PFGE) analysis of the isolates, the results showed that different isolates belonged to the same serotype, their pathogenicity island gene profiles were identical, and their PFGE profile similarities were more than 95%, which implied that the same serotype isolates with high homology, so we choose a representative strain of each serotype as the tested strain in the challenge experiments.Then we select representative isolates to infect 6-8 week old KM mice at a dose of 108CFU by intraperitoneal injection, only the S. typhimurium strain inoculated mice died, the remaining isolates were not lethal to mice after infection. Through the determination of LD5o and colonization and persistence of the bacteria in vivo experiment, we compare the difference of pathogenicity between Salmonella choleraesuis strain and Salmonella typhimurium isolate, the results showed that lethal dose of Salmonella typhimurium was nearly 200 times higher than that of Salmonella choleraesuis, however, when the bacteria entered the mouse body, the proliferation and distribution of Salmonella typhimurium was more quick than that of Salmonella choleraesuis, bacteria reached peak 6 h post-challenge, then decreased gradually. S. typhimurium can cause acute death during a week post-challenge, no deaths have been observed since a week. Salmonella choleraesuis was fatal infection for mice but caused their death slowly, course of infection was long, and the survivals could shed bacteria in a long time, after a month of infection the bacteria can still be detected in the intestine and feces of challenged mice.