Development Of Inactive Vaccine Of Streptococcus Suis Serotype 2

Streptococcus suis(S.suis)is an important zoonotic pathogen that can cause widespread infections in pigs and humans,manifested as meningitis,sepsis,arthritis and endocarditis.Among the 33 serotypes,Streptococcus suis type 2(SS2)has the most widespread epidemic,the most pathogenicity and the most serious damage,causing huge economic losses to the breeding industry and endangering public health security.At present,the research and development of the vaccine against Streptococcus suis type 2 mainly focuses on the research and development of subunit vaccines.However,there are many SS virulence factors and it is impossible to form an effective immunoprotective effect with only one or two virulence factor-expressing proteins.Therefore,the whole-cell inactivated vaccine still has an irreplaceable effect.At the same time,it is of great significance to develop a safe,highly effective,cross-protective inactivated vaccine for the prevention of swine streptococcosis.1.Isolation,identification and biochemical assay of Streptococcus suis type 2PCR was used to identify Streptococcus suis type 2 isolated from the clinic,which were NT151,NT155,NT157,NT15B,NT15D,and NT15J,respectively.And we studied the physical and chemical characteristics of each strain in terms of growth characteristics,biochemical characteristics,drug resistance,virulence genes.From the perspective of growth characteristics,biochemical characteristics,and virulence genes,there was no significant difference between the isolates and the reference strain ZY05719;from the point of drug resistance,NT15B and NT15D strains showed double drug resistance,and other strains only had one antibiotic.Resistant,and all strains are sensitive to penicillin and third generation cephalosporin antibiotics.It provides the basis for clinical use and further study of the virulence of each strain.2.Pathogenicity of Streptococcus suis type 2 isolatesThe virulence of SS2 NT151,NT155,NT157,NT15B,NT15D,NT15J and ZY05719 against zebrafish and mice was compared by intraperitoneal injection.We known that NT15B has the strongest virulence among isolates,second to ZY05719 strain.The median lethal doses to zebrafish of each strain are:ZY05719 LD50=9.32×104 CFU,NT15B LD50=5.37×105 CFU,NT151 LD50=6.32×105 CFU,NT155 LD50=8.22×105 CFU,NT157 LD50=7.65×105 CFU,NT15D LD50=6.67x105 CFU,NT15J LD50=9.38×105 CFU.Therefore,the NT15B strain was selected as a vaccine candidate strain to establish a basic seed lot.For the next step in the development of inactivated vaccines and piglet immune protection tests provide strains and references.3.Preparation of Inactivated NT15B Vaccine and Its Effect on Piglet ImmunityNT15B water adjuvant inactivated vaccine successfully prepared on the basis of purely safety checks and tests are carried out on pigs immune protection.In the immunization duration test,blood was collected from the vena cava at 1d,7d5 14d,and 21d after exemption,1d,7d,14d,and 21d after the second exemption.Serum antibodies were detected using a Streptococcus suis type 2 indirect ELISA kit.In piglet immune protection trials,the trials were divided into 3 groups:1 group was NT15B vaccine group,2 groups were commercialized vaccine groups,and 3 groups were negative control groups.The results showed that NT15B water adjuvant vaccine and commercial vaccine had good protective effect on piglets and the protection rate was 100%.The experiment provides data support and certain reference value for clinical inactivated vaccine research.