猪链球菌4型疫苗用菌株的筛选

Screening of strains for inactivated vaccine against Streptococcus suis serotype 4

【背景】猪链球菌4型(Streptococcus suis serotype 4,SS4)分离率日益升高,对养殖业和公共卫生安全造成严重危害,目前尚无有效的SS4疫苗。【目的】筛选致病力强、抗原性好、遗传性状稳定的SS4疫苗菌种。【方法】以7株SS4分离株(代号为A1−A7)为受试菌株,通过累积法测定菌株半数致死量(LD_(50)),ELISA测定免疫小鼠血清中IgG效价,攻毒保护试验测定免疫保护率,并采集小鼠脏器观察病理组织学变化。再连续传代培养受试菌株,分别对第10、20、30代菌株进行致病性和抗原性试验。【结果】A1−A7菌株对小鼠的LD_(50)分别为2.19×10^(8)、1.76×10^(8)、1.83×10^(8)、1.01×10^(8)、4.05×10^(8)、1.19×10^(8)和9.03×10^(7) CFU。二免7 d后,A1、A2、A3、A4、A6、A7免疫组IgG效价分别为1:1600、1:1600、1:3200、1:6400、1:3200和1:6400,免疫保护率分别为30%、30%、50%、70%、60%和80%,而且A4、A7免疫组小鼠组织病变较其余4组轻微。体外传至30代后,A4菌株的LD_(50)上升至3.81×10^(8) CFU,IgG效价下降至1:1600,免疫保护率下降至40%,而A7菌株的LD_(50)上升至2.49×10^(8) CFU,IgG效价和免疫保护率稳定保持为1:6400和80%,而且A7免疫组小鼠的组织病变较A4免疫组轻微。【结论】A7菌株(原始编号为HBgu18-4)具有强致病力和良好的抗原性,而且遗传性状均一、稳定,可作为SS4制苗候选菌株。

[Background]The increasing isolation rate of Streptococcus suis serotype 4(SS4)causes serious harm to animal farming and public health,and there has been no effective vaccine for SS4 so far.[Objective]The purpose of this research was to screen out SS4 vaccine strains with strong pathogenicity and desirable antigenicity and genetic stability.[Methods]Seven SS4 isolates(code A1–A7)were selected as the tested strains.They were determined for the half lethal dose(LD_(50)),the IgG titer in serum of immunized mice and the immune protection rate by Reed-Muench method,enzyme-linked immunosorbent assay(ELISA)and challenge assay,respectively.Meanwhile,the histopathological changes of the mice organs were observed,and after continuous subculture,the 10th,20th,30th generations of the tested strains were subjected to pathogenicity and antigenicity tests.[Results]The LD_(50) of A1–A7 for the mice were 2.19×10^(8),1.76×10^(8),1.83×10^(8),1.01×10^(8),4.05×10^(8),1.19×10^(8),and 9.03×10^(7) CFU,respectively.After 7 days of secondary immunization,the IgG titers of A1,A2,A3,A4,A6,and A7 immune group were 1:1600,1:1600,1:3200,1:6400,1:3200 and 1:6400,respectively,and the immune protection rates were 30%,30%,50%,70%,60%and 80%,respectively,with the pathological changes of A4 and A7 immune groups being milder than the other immune groups.After in vitro passing to the 30th generation,the LD_(50) of A4 increased to 3.81×10^(8) CFU,and the IgG titer and the immune protection rate decreased to 1:1600 and 40%.By comparison the LD_(50) of A7 elevated to 2.49×10^(8) CFU,and the IgG titer and the immune protection rate remained stable at 1:6400 and 80%.Additionally,the pathological changes of A7 were milder compared with those of A4.[Conclusion]A7(original number HBgu18-4)had strong pathogenicity and good antigenicity,with uniform and stable genetic traits.It could be used as a candidate strain for SS4 vaccine.