Isolation And Identification Of Streptococcus Suis Type 9 CZ16A Strain And Preparation Of Inactivated Vaccine

Swine streptococcosis is an important infectious disease in swine industry.Meningitis,sepsis and arthritis are the main features in clinical practice.It leading major economic losses wordwide and bringing huge challenges to the pig industry.There are 33(1?31,33 and 1/2)serotypes of S.suis which can be divided into highly pathogenic,weakly pathogenic(low pathogenic)and non-pathogenic.(Non-toxic)strains according to their virulence.In general,S.suis serotype 2(SS2)is considered to be the most virulent and frequent isolated serotype in clinically ill piglets.S.suis serotype 9(SS9)is one of the segregating serotypes.There are no effective prevention and control strategy against swine streptococci,and there is no commercial vaccine for SS9.The development of safe and effective vaccines is an effective strategy to prevent S.suis infection.The purpose of this study was to develop an inactivated vaccine against SS9.The SS9 strain CZ16A used in this study was isolated from the infection effectively tonsils of infected pigs.The inactivated vaccine constructed in this study could provide good protection in mice and piglets.This article systematically studied the biological characteristics of CZ16A strain and the protective efficacy of SS9CZ16A inactivated vaccine in mice and piglet.1.Biological characteristics of the strain CZ16A:A major pathogen CZ16A was isolated from the tonsils of a diseased pig in a pig farm in Changzhou.Characters of the strain were studied such as serotype,Gram stain,virulence factor,biochemical reaction,and drug susceptibility.Therefore the growth curves,the relationship between colony-forming units(CFU)and OD values,and virulence were studied.The results showed that this strain was identified as S.suis type 9 by gdh and cps9h double PCR and gram staining.The virulence factors of the strain were MRP-/EPF-and SLY+/FBPS+/GAPDH+/ORF+,The bacteria would be grown to the logarithmic phase in hours and the viable cells could up to 2.85 X 109CFU in 6 h in fresh medium.The zebrafish as model animals were divided into five gradients and the highest dose was 1.44 × 107CFU.The mouse as model animals were divided into five gradients and the highest dose was 5.6 × 108CFU.The virulence of CZ16A strain was determined with LD50 in zebrafish model and the LD50 is 2.13 X 103CFU however the LD50 is 9.55 × 105CFU in mice model.2.The efficacy of the inactivated vaccine SS9CZ16A against mice and piglets:there was no death in piglets challenged with virulent SS9CZ16A at the dose of 6 × 108CFU.However,all the piglets showed typical clinical symptoms such as meningitis and arthritis.The SS9 inactivated vaccine was prepared with inactivated with 0.4%formaldehyde at 28? for 12 h with the addition of GEL water adjuvant.The sterility assay was used to test the vaccine quality.The mice and piglets were immunized and challenged and the results showed that 80%of mice were survived with the protection of inactivated vaccine at the dose of 2 × 107CFU.The piglet control group showed lesions of varying degrees and the most severe diseased piglets showed severe pericardial adhesions,bleeding points,There was in,meninges,heart and liver to different degrees in the immunization group,however,there was a infected piglets a slight splenic adhesion.These results showed that the inactivated vaccine developed in this experiment could provide protection to piglets against virulent SS9.The biological characteristics of the isolated strain CZ16A,and the immune protection of the inactivated vaccine in mice and piglets were explored in this study.This study lays the foundation for establishing an effective prevention and control system against S.suis and provides scientific basis for mass production of commercial vaccines.