| ObjectiveIn order to clarify the dominant serotypes of Salmonella in the Liaoning pig production chain and their pathogenic and drug resistance characteristics,explore and analyze the distribution and spread of virulence factors and drug resistance genes in different serotypes of Salmonella in the pig production chain,and develop a large-scale pig farm Research on detection and distribution of Salmonella serotypes,virulence factors,drug resistance and drug resistance genes in slaughterhouses and sales links,on the one hand,it provides a basis for exploring the transmission mechanism of Salmonella suis,and on the other hand,it establishes an effective pig production chain control of Salmonella Measures provide the basis.MethodsFrom 2017 to 2018,a representative large-scale pig farm was selected from Liaoning Province,and samples of diarrheal disease pig anal test strips,fecal samples of pigs to be slaughtered in downstream pig slaughterhouses,carcasses of corresponding slaughter links,and pork segmented in the sales market were collected.The collected samples were first identified by Salmonella microbiologically;at the same time,the conserved gene Salmonella invA was used for molecular biological identification,and the serum factor-specific gene PCR identification and factor serological identification methods were used to determine the serotype of Salmonella suis isolates.;The main virulence factors of Salmonella suis of different serotypes were detected by PCR method and their distribution characteristics were compared and analyzed.To test and observe the pathogenicity of Salmonella suis of different serotypes by using mouse challenge test and pathological techniques,and to compare and analyze the pathogenicity of different serotypes of strains;to perform drug sensitivity tests and drug resistance genes on the isolated strains Detection and comparison of drug resistance profiles of isolated strains of different production stages and different serotypes,and finally the distribution characteristics and transmission of Salmonella drug resistance genes.Results1.The detection rates in pig farms,slaughterhouses,and sales markets were 8.7%,10.89%,and 8.57%.There are three main serotypes of Salmonella in each link,which are swine cholera,enteritis,and typhoid typhoid.The predominant serotypes in the link are basically the same,but the detection rates are different.For example,the highest detection rate of Salmonella enteritidis in the farm,and the highest detection rates in the slaughterhouse and sales market are Salmonella suis cholera and Salmonella typhimurium,respectively.2.Pathogenicity tests show that Salmonella choleraesuis can cause acute sepsis in mice,with a mortality rate of up to 100%.Both Salmonella enteritidis and Salmonella typhimurium can cause disease in mice,but the damage to all organs is lighter,and the mortality is all It is as high as 33.3%,which confirms that the pathogenicity of different serotypes of Salmonella suis is quite different.Salmonella choleraesis has the highest pathogenicity and extensive and severe organ damage.3.Salmonella virulence factors were detected in three major links in the pig production chain,including spvR,spvA,mogA,mgtC,araB,stn,sseL,and bcfA.There are 6 virulence factors carried by the three links.They are spvR,spvA,mogA,mgtC,araB,and stn,which prove that the main virulence factors of Salmonella have been widely distributed and transmitted in different links of the pig production chain,thereby maintaining their pathogenicity.There are 6 virulence factors carried by the three serotypes,including all virulence island genes and enterotoxin genes.Plasmid virulence factors were detected by Salmonella typhimurium,and 9 and 12 viruses were detected by Salmonella cholerae and Salmonella enteritidis,respectively.Force factor.This shows that different serotype virulence factors have both commonalities and differences.Virulence island genes and enterotoxin genes are related to their pathogenicity,while other genetic differences may be related to their pathogenicity differences.4.There are five kinds of drugs that have drug resistance in pig farms,slaughterhouses,and sales markets,which proves that Salmonella has developed serious drug resistance in the pig production chain and passed on.Salmonella of swine origin has a resistance rate of more than 50%to five of the six drugs.There are differences in the drug resistance of Salmonella in different parts of the slaughterhouse:pigs to be slaughtered>Carcass>Liver>Sewage>Slaughtering tools,which may be related to the spread between different links in the slaughterhouse and the abuse of antibacterial drugs by breeders in the farm.Drugs with a high rate are commonly used drugs in production practice.Drugs that still maintain sensitivity are infrequently used and unused drugs,indicating that the development of drug resistance is closely related to the frequency of drug use.5.Five of the 12 major drug-resistant genes of salmonella derived from pigs had a detection rate of more than 50%,which were gyrA100%,gyrB100%,TEM97.43%,sul3 94.87%,and floR58.97%.Pig farms,slaughterhouses and sales markets carry eight types of drug resistance genes,which are related to fluoroquinolones,florfenicol,tetracyclines,β-lactams,and sulfonamides,among which are gyrA and gyrB genes.The detection rate reached 100%.More than 50%of the resistant genes were detected in more than half of the total number of resistant genes detected,indicating that the major resistant genes were transmitted at different stages,and the resistant phenotype was basically the same as the results of the resistant gene test.Conclusions1.Salmonella is widely distributed in Liaoning pig production chain,and its dominant serotypes are Salmonella cholerae,Enteritis,and Typhoid.2.There are 9 kinds of virulence factors carried together in the three links of the pig production chain.The virulence factors are transmitted in the pig production chain.Different serotypes have different types and numbers of virulence factors,and differences in virulence factors lead to differences in pathogenicity.3.Salmonella spp.from different stages has developed serious resistance to common veterinary drugs and has been transmitted.The main drug resistance genes are widely distributed and spread in different links and different serotypes of Salmonella.The widespread spread of drug resistance genes in Salmonella leads to the spread of drug resistance. |
