Molecular Typing And Virulence Evaluation Of Streptococcus Suis Isolated From Domestic Farm Sick Pigs

Streptococcus suis is the general name of swine diseases caused by Streptococcus equi,Streptococcus equi,Streptococcus D,E,L and Streptococcus suis?SS?.The main clinical manifestations are septicemia,pyogenic lymphadenitis,pneumonia,meningitis and arthritis.Streptococcus suis is a common and frequently occurring disease in pig production.In the past 20 years,with the development of large-scale pig industry,the incidence of Streptococcus suis has been increasing,and it has been infected or mixed with some other diseases,such as blue ear disease,Porcine Circovirus Disease,swine fever,pseudorabies,Haemophilus parasuis disease,infectious pleuropneumonia and so on,which leads to a significant increase in the mortality rate and a large economic loss to pig production.Therefore,Streptococcus suis will be listed as the second class animal disease in the agricultural and rural areas of China.SS is the main cause of Streptococcus suis.Different serotypes lack mutual immunity.The genotypes are complex and diverse.There are genetic differences between different strains,and the virulence is also different,which brings great trouble to the prevention and control of Streptococcus suis.The purpose of this study is to investigate the distribution characteristics of serotypes,virulence genotypes,multi site sequence typing?MLST?and virulence evaluation of 55 SS isolates from family farms in Anhui,Jiangsu,Shandong,Hebei,Guangxi and other five provinces of a group company.The purpose of this study is to explore the distribution characteristics of serotypes,virulence genotypes and MLST genotypes of SS and the relationship between them and virulence,so as to serve as the group company To provide reasonable basis and technical support for scientific prevention and control of Streptococcus suis.In this study,55 SS isolates were used as the test strains for the following tests:?1?35 serotype specific primers for SS were synthesized and serotyped by PCR;6virulence genes?mrp,epf,sly,orf2,fbps,gapdh?primers for SS were synthesized and the virulence genes of SS isolates were genotyped by PCR;7 housekeeper genes?aro A?cpn60?dpr?gki?mut S?rec A?thr A?for SS were synthesized and the virulence genes of SS isolates were genotyped by PCR,and UPGMA phylogenetic tree was constructed to analyze the relationship between the isolates in different regions.?2?Kunming mouse was used as animal model to test the pathogenicity of SS isolate.The isolate with 100%lethality was screened out and LD₅₀was determined by accumulation method.The results showed that:?1?there were 9 serotypes and no serotypes in 55 SS isolates,SS4 was the dominant serotype,19 strains,accounting for 34.5%;there were11 virulence genotypes,epf-mrp-sly-gapdh+fbps+orf2+,16 strains,accounting for29.1%;the dominant virulence genotype of SS4 was epf+mrp+sly+gapdh+fbps+orf2+;there are 21 ST types,ST94 is the dominant st type,21 strains,accounting for 38.2%.Among them,11 ST types are found for the first time,there are more than3 allele mutations,most of the same ST type SS isolates can only correspond to one serotype,but there are multiple ST types in the same serotype isolates,ST1229?Jiangsu and Hebei isolates?is closely related to ST1233?Shandong isolates?,and ST94?Anhui isolates?is closely related,Jiangsu and Hebei isolates)were closely related to ST108?Hebei and Jiangsu isolates?.?2?Among the 55 SS isolates,11 were selected with a mortality rate of 100%.They were HBgu18-3?SS4??HBgu18-4?SS4??AHhuai18-10?SS4??AHhuai18-8?SS4??JSxu18-4?SS4??AHfu18-1?SS7??HBgu18-2?SS7??AHshou18-1?SS4??JSbin18-1?SS8??JSxu18-10?SS4??JSbin18-8?SS8?.Their LD₅₀were 3.39×10⁸CFU/m L?3.54×10⁸CFU/m L?4.57×10⁸CFU/m L?5.01×10⁸CFU/m L?5.17×10⁸CFU/m L?5.37×10⁸CFU/m L?5.62×10⁸CFU/m L?1.0×10⁹CFU/m L?1.67×10⁹CFU/m L?3.0×10⁹CFU/m L?4.47×10⁹CFU/m L?The results showed that:?1?The serotypes of SS prevalent in family farms in five provinces and regions of the group company are complex,SS4 is the dominant serotype;the virulence genotype is diverse,epf-mrp-sly-gapdh+fbps+orf2+is the dominant virulence genotype,epf,mrp,sly are mainly present in SS4,while gapdh,fbps,orf2 are widely present in various serotypes of SS;ST genotype is diversified Trend:st94 is the dominant st type,with obvious genetic variation,high degree of intraspecific differentiation,a certain degree of cross with serotypes,and the isolates in the adjacent areas have high homology.?2?There are 8 virulent strains,1medium virulent strain and 2 weak virulent strains in the family farms of the five provinces of the group company.Among them,SS4 is the most virulent strain,followed by SS7 and SS8;ST94 is the most virulent strain in the same serotype;most of the isolates carry more virulent gene types,the more virulent they are.