关键词：转移酶类；链球菌；变异；牛奶
【摘要】 目的 了解免疫乳清对变形链球菌葡萄糖基转移酶（glucosyltransferase,GTF）活性的影响。方法 免疫乳清来源于GTF 过表达株B-29-33免疫孕牛中获得的牛奶。对照乳清从未免疫孕牛中获得。用gtf B基因缺陷株B-29吸收免疫乳清中的抗体获得免疫吸收乳清。采用蒽酮定糖法检测3种乳清在50、70及90 μl 3种剂量条件下对GTF合成水不溶性葡聚糖的影响。结果 对照乳清具有增强酶活性的作用，可使酶活性增强3倍以上。免疫吸收乳清可部分抑制这种增强作用。免疫乳清可完全抑制乳清对酶活性的增强作用，并在此基础上抑制GTF的活性。结论 免疫乳清可以有效抑制 GTF合成水不溶性葡聚糖。其抑制作用可能与乳清中所含的抗GTF 特异性抗体有关。
The effect of immune bovine whey on cell-associated glucosyltransferase activity of Streptococcus mutans
CHEN Wenxia, FAN Mingwen, BIAN Zhuan, et al.
(Department of Operative Dentistry,Cariology and Endodontology, School of Stomatology, Hubei Medical University, Wuhan 430079, China)
【Abstract】 Objective To study the effect of immune bovine whey on cell-associated glucosyltransferase (GTF) activity of S.mutans MT8148.Methods The immune milk was collected from cows immunized with cell-associated GTF overexpression strain B-29-33 of S.mutans MT8148. The control milk was from non-immunized cows. The immune absorbed whey was gotten from immune bovine whey which was absorbed with lyophilized Formalin-killed B-29 whole cells. Three kinds of whey were subdivided into three groups: 50 μl、70 μl、90 μl. The content of insoluble glucan was estimated colorimetrically by anthrone method.Results The control bovine whey had an enhancing GTF activity (407.00%～485.62%). The immune absorbed whey inhibited partly the enhancing GTF activity (208.74%～273.00%). The immune whey inhibited significantly the GTF activity (70.24%～38.62%) and the inhibition showed a tendency to depend on doses.Conclusions The immune bovine whey inhibits significantly the cell-associated GTF activity of S.mutans MT8148.
【Key words】 Transferases； Streptococcus mutans ； Milk
变形链球菌（下简称变链菌）对牙面的粘附和定居是致龋的始动因子。变链菌所产生的葡糖基转移酶（glucosyltransferase， GTF）被认为是主要的致龋毒力因子之一。GTF能以蔗糖为底物，合成2种葡聚糖，即水溶性和水不溶性葡聚糖。水不溶性葡聚糖（isoluble glucan，ISG）因其非水溶性和粘性，在细菌粘附中起重要作用。我们的研究目的是体外观察免疫乳清对变链菌GTF合成ISG活性的影响。
材料和方法
1．细菌：本研究所使用的菌株为S.mutans MT8148（国际标准株）和B-29。B-29为本实验室以S.mutans MT8148为亲代株，采用基因工程手段构建的gtfB基因缺陷株［1］。
2．免疫乳清和对照乳清的制备：本项研究所使用的免疫牛奶来源于边专等［2］用细胞结合型GTF过表达株B-29-33单株全菌疫苗免疫孕牛获得的免疫牛奶。对照牛奶来源于同一饲养场未免疫奶牛的牛奶。根据Michalek等［3］介绍的方法制备免疫乳清和对照乳清。
3．免疫吸收乳清的制备：B-29在含红霉素（10 mg/L）和卡那霉素（250 mg/L）的MSB和TTY培养基中培养及增菌，0.5％甲醛灭活，调节菌浓度至A450=1，取1ml菌液冻干成粉，加入1 ml免疫乳清混匀。4℃冰箱放置48 h，离心。上清即为免疫吸收乳清。
