牛源金黄色葡萄球菌突变株的筛选、鉴定及其免疫原性的研究

 【目的】诱变牛源金黄色葡萄球菌山东分离株(zfb),筛选、鉴定弱毒性突变株,并研究其在鼠上的免疫交叉保护性。【方法】牛源金黄色葡萄球菌山东分离株zfb,经N-甲基-N'-硝基-N-亚硝基胍(MNNG)化学诱变,经生长特性、回复突变、毒力检测、LD50、多种特征性酶检测、小鼠中免疫保护性等实验比较研究了突变株与亲本株的生物学特性,筛选得到遗传性状稳定β－溶血素缺失的弱毒性突变株。【结果】弱毒性突变株Hx与亲本株相比：其β－溶血性状完全缺失,生长缓慢,耐热核酸酶、血浆凝固酶等胞外蛋白的产量减少,在活体条件下可产生荚膜,半数致死量(LD50)10－1.83•mL-1远低下于亲本株的10－4.33•mL-1。亲本株保护检测,免疫接种过的鼠的半数致死量是未接种过的6—50倍。非亲本株保护检测,免疫接种过的鼠的半数致死率是未接种过的5—60倍。【结论】突变株Hx的β－溶血素缺失,毒性减弱,对金黄色葡萄球菌攻击具有较高免疫保护性。

Screening an Attenuated Strain and Immunogenicity in Mice of a Bovine Mastitis Staphylococcus Aureus Mutant

Objective] The objective of the study was to screen an attenuated strain and immunogenicity in mice of a bovine astitis Staphylococcus aureus mutant.Method] An attenuated mutant, designated Hx,was derived from Staphylococcus aureus bovine mastitis strain SA zfb after N-methyl-N'-nitro-N-nitrosoguanidine mutagenesis.The characteristics were tested and the protection experiments were carried out by intraperitoneal administration in mice and challenged with homologous and heterologous strains.Result] Mutant Hx,which was isolated on the basis of hypotoxicity, showed diminished virulence in mice(LD50 of SA Hx:10-1.83·mL-1,LD50 of SA ztb:10-4.33·mL-1).Mutant Hx grew more slowly than its parental strain and showed decreased production of several exoproteins,such as a-and -hemolysin,DNAse and coagnlase.The production of its capsule was induced only under in vivo growth conditions.In homologous challenge,the LD50 of SA zfb in mice immunized with different doses of the mutant was about 6 to 50 times higher than that of untreated mice.In heterologous challenge,the LD50 of SA 25923 and the LD50 of SA L20-2 in mice immunized with different doses of the mutant was about 5 and 60 times higher than that of untreated .Conclusion] The fact shows that mutant Hx is attenuated and that it confered in mice immunity against homologous and heterologous strains,so it is an interesting candidate for tbe preparation of a live-attenuated vaccine against staphylococcal infections.