Isolation And Identification Of Swine Streptococcus Type 3 And Study On Its Capsular Polysaccharide Vaccine

Streptococcus suis is a kind of gram-positive cocci with capsule,which can cause septicemia,arthritis and dyspnea in pigs of different ages,breeds and genders.Capsular polysaccharide is the main protective antigen and virulence factor of bacteria.It has good immunogenicity and is one of the most suitable bacterial target antigens for vaccine.In order to know whether the capsular polysaccharide of Streptococcus suis has immune effect on Streptococcus suis,a Streptococcus suis was isolated from a pig farm in Tianjin.It was identified as type 3 Streptococcus suis by 16 Sr RNA,and carried virulence factors such as srt A,ORF2,GAPDH,abpb,SNA,LMB,znua,gdhgdh,EPF,MRP,etc.The growth curve showed that the growth of the strain reached the peak at 9h-10h(log CFU = 9.4);the drug sensitivity test showed that the isolate was sensitive to amoxicillin,cephalosporins,and resistant to florfenicol,lincomycin,etc.;it had strong pathogenicity to mice,and the lethal rate reached 100% within 48 h after infecting mice with the maximum lethal dose.The content of type 3 capsular polysaccharide was 34.21% by phenol sulfuric acid method.Protease K,DNase I and RNase A were used to remove the protein and nucleic acid from the crude polysaccharide.The protein content was below 100 ug / m L and the nucleic acid content was below 0.125mg/m L.The purified polysaccharide was obtained by freeze-drying.40 Kunming mice were randomly divided into 5 groups.The mice were immunized with capsular polysaccharide solution,and the positive control group and the blank control group were set.The positive control group was immunized with general vaccine of Streptococcus suis type 2 and 7,and the blank control group was injected with PBS solution.After two times of immunization,the virus was attacked.Results the immune protection rate was 75%in the high concentration group.62.5% in the middle concentration group,50% in the low concentration group,37.5% in the positive control group,and all died in the negative control group.All mice were observed by histopathology.At present,there are not only two types of Streptococcus which are prevalent in pig farms,but also the prevention of Streptococcus.This experiment shows that the capsular polysaccharide vaccine can give a certain degree of protection and is higher than the general weak virus vaccine on the market,which has made a certain contribution to the prevention and control of Streptococcus.