pH值对磁性固位体耐蚀性能的影响

目的　研究人工唾液的酸碱度在偏酸性的条件下,3种磁性固位体外包裹容器的耐腐蚀能力的改变。方法　将3种磁性固位体浸泡于人工唾液中,介质pH值分为5·6和7·0两组,实验温度36·5℃,时间6个月。采用恒电位法测定极化曲线实验、浸泡实验及扫描电镜方法,分析材料的耐腐蚀能力。结果　pH值下降,磁性固位体外包裹容器---不锈钢中铁离子的溶出量提高近10倍。表明在偏酸性的环境中,3种材料的腐蚀速度都加快。结论　磁性固位体的耐酸性能力相对较差,这将影响他们的使用寿命。     

Sorbitol transport by Streptococcus sanguis 160

Sorbitol metabolism was examined with a sorbitol-fermenting strain (160) of Streptococcus sanguis isolated from the dental plaque of a subject using sorbitol-containing chewing-gum for 4 years. S. sanguis 160 was grown in continuous culture (pH, 7.0; dilution rate, 0.1 h-1) with glucose, sorbitol and nitrogen (sorbitol-excess) limitations. Cells grown with a glucose limitation exhibited low, but detectable, uptake of [14C]-sorbitol and transition to medium limiting in sorbitol resulted in a 5-fold increase in sorbitol uptake. Kinetic data revealed that both glucose and sorbitol-limited cells possessed 2 transport systems for sorbitol (Ks = 3.3-6.7 and 36-64 microM), but continued growth of the organism on limiting sorbitol resulted in the loss of the high-affinity system. Decryptified, sorbitol-limited cells phosphorylated sorbitol in the presence of phosphoenolpyruvate (PEP), but not with ATP, indicating sorbitol transport solely via the PEP phosphotransferase (PTS) system. PEP-dependent activity in glucose-limited and sorbitol-excess cells was 6- and 4-fold lower than that of the sorbitol-limited cells. Uptake of [14C]-sorbitol and activity for Ell for sorbitol [Ellsor] of the PTS in cells in transition from a glucose to sorbitol limitation confirmed the induction of the sorbitol-PTS and the repression of the glucose-PTS in the presence of sorbitol. Cells grown with an excess of sorbitol exhibited very low Ellsor activity. A crossover experiment with membranes and soluble fractions from glucose-, sorbitol- and nitrogen-limited cells of S. sanguis 160 demonstrated the induction of a soluble PTS component in sorbitol-limited cells essential for sorbitol transport via the PTS.(ABSTRACT TRUNCATED AT 250 WORDS)     

血链球菌产生过氧化氢能力的差异

目的：初步研究血链球菌产生过氧化氢的能力，筛选过氧化氢高产菌株。方法：从牙周健康人群口腔中收集血链球菌，采用酚红—辣根过氧化物酶微量板法测定细菌产生过氧化氢的量，并测定细菌的蛋白含量以定量观察血链球菌产生过氧化氢的能力。结果：每微克菌蛋白的血链球菌Ⅱ型(又称为口腔链球菌，Streptococus oralis,S.oralis）产生过氧化氢的量高于血链球菌I型(Streptococcus sanguis,S.sanguis)(P＜0．05)；有氧培养时血链球菌比厌氧培养产生更多的过氧化氢(P＜0．05)；和国际标准株S．oralis ATCC10557相比，S．oralis临床分离株l～12能稳定地产生较高的过氧化氢。结论：血链球菌在有氧和厌氧情况下都能产生过氧化氢，有氧时产生过氧化氢的能力更强；S．oralis产生过氧化氢的能力高于S．sanguis，同一种细菌的不同株之间产生过氧化氢的能力有很大差异。血链球菌产生过氧化氢的机制需进一步研究。     

In vitro development of chlorhexidine resistance in Streptococcus sanguis and its transmissibility by genetic transformation

Three chlorhexidine-sensitive strains of Streptococcus sanguis developed resistance to chlorhexidine when grown as continuous cultures in a fermenter containing medium with increasing concentrations of the drug. The MIC of the test strains increased by between two and three dilution steps and these high values were maintained after daily transfer in drug-free medium for at least 15 d. In addition, the resistance of one of the strains persisted for more than 1 month of continuous growth in drug-free medium in the fermenter. DNA from the resistant (Chx¹) variants of the three strains transformed competent sensitive S. sanguis to increased chlorhexidine resistance, thus proving that resistance to this drug is an inheritable trait. Immunoelectrophoretic experiments showed that certain changes in the antigenic pattern of the Chx¹ variants had occurred as compared with their sensitive wild-type strains. Antigen extracts of the Chx¹ variants and all Chx¹ recombinants tested contained consistently less protein than those of the sensitive wild-types.     

牙周可疑致病菌对血液链球菌产生过氧化氢的影响

目的：了解牙周可疑致病菌对血液链球菌产生过氧化氢的影响，探讨血液链球菌产生的过氧化氢在牙周微生态环境中的作用。方法：采用酚红还原－微量反应板法检测粘性放线菌（Ａｖ）和４种牙周可疑致病菌即牙龈紫质单胞菌（Ｐｇ）、具核梭杆菌（Ｆｎ）、中间普氏菌（Ｐｉ）、伴放线放线杆菌（Ａａ）与血液链球菌混合孵育后上清中的过氧化氢含量变化。结果：在不加外源性糖作为底物时，仅Ｆｎ组有高于对照组的过氧化氢，Ｐｇ、Ｐｉ、Ａａ组均未能测出。在有葡萄糖、蔗糖、麦芽糖、乳糖存在时，Ｐｉ、Ａａ组无过氧化氢积累，Ｐｇ、Ａｖ、Ｆｎ组能检出的过氧化氢含量也低于对照组。结论：本实验中Ａｖ和其它４种牙周可疑致病菌均可导致血液链球菌产生过氧化氢的量下降，提示在牙周微生态环境中，这些细菌可能利用血液链球菌产生的过氧化氢或影响过氧化氢的产生。     

影响血链球菌粘附因素的研究

目的 探讨ＰＨ值、钙离子对血链球菌粘附至血清,包被羟磷灰石的影响。方法 采用Ｃｌａｒｋ创立的体外粘附实验模型,以「＾３Ｈ」胸腺嘧核标记对血锭球菌的粘附进行定量观察。结果不同ＰＨ值组测得的放射性测量计数率差异有显著性;其中ＰＨ值为６．０－７．５时ｅｐｍ值最高,ＰＨ值小于５．５时ｅｐｍ则明显降低。不同钙离子浓度的实验组ｃｐｍ值均显著高于对照组,当钙离子浓度为１．２５３．７５ｍｍｏｌ／Ｌ时ｅｐｍ了高。结     

Sorbitol inhibition of glucose metabolism by Streptococcus sanguis 160

Clinical studies in Sweden have shown that the proportion of sorbitol-utilizing strains of Streptococcus sanguis increases in dental plaque from individuals using sorbitol-containing products for prolonged periods. We have undertaken to study the metabolism of glucose and sorbitol by S. sanguis 160, isolated from a subject consuming sorbitol-containing chewing-gum 4 times a day for 4 years. Growth on glucose was inhibited by the presence of sorbitol in the growth medium and sorbitol was utilized in the presence of glucose, albeit, at a slower rate than glucose. In addition, pulses of glucose added to cultures growing on sorbitol resulted in the expulsion of sorbitol from the cell. In order to examine further the relationship of sorbitol and glucose, uptake assays were carried out with S. sanguis 160 grown in continuous culture (pH 7.0, dilution rate = 0.1 h-1) with glucose, sorbitol or nitrogen (sorbitol excess) limitations. The uptake of [14C]-glucose by sorbitol-limited cells, but not by glucose-limited cells, was inhibited by sorbitol, as was glycolysis. Kinetic experiments with glucose-limited cells showed 2 transport systems for glucose with Ks values of 5.2 and 40 microM, and glucose phosphorylation activity by decryptified cells indicated transport by the P-enolpyruvate (PEP) phosphotransferase system (PTS) with lesser activity for an ATP-dependent transport process. Transition from glucose-limited growth to sorbitol-limited growth revealed repression of total [14C]-glucose uptake by intact cells and activity for Enzyme II for glucose (Ellglc) of the PTS measured in membrane preparations in the presence of an excess of the soluble PTS proteins in crude cell-free supernatant fractions.(ABSTRACT TRUNCATED AT 250 WORDS)     

不同分子量的壳聚糖对血链菌生物膜的脱落作用

目的:观察不同分子量的壳聚糖促进血链菌生物膜表面的脱落作用。方法:在模拟人口腔环境的人工口腔内,形成4h血链菌生物膜,分别放入黏度5cps(小分子量)、80cps(中分子量)和600cps(大分子量)的2%壳聚糖溶液中,作用时间为3、10、30min,然后应用激光共聚焦扫描显微镜和死菌/活菌荧光染色技术相结合,比较其促进血链菌生物膜表面脱落的作用,对所得数据进行方差分析。结果:壳聚糖应用于4h血链菌生物膜,可以有效促进细菌脱落(P<0.05),黏度5cps(小分子量)的壳聚糖的作用效果最好(P<0.01)。结论:黏度5cps(小分子量)的壳聚糖是一种有效促进菌斑生物膜脱落的药物。     

Effect of chlorhexidine on the relative proportions of Streptococcus mutans and Streptococcus sanguis in hamster plaque

abstract — The effect of chlorhexidine on the proportions of Streptococcus mutans and Streptococcus sanguis in plaque was studied in hamsters fed a diet containing 28% sucrose. In animals given chlorhexidine in their drinking water for 10 d a decrease in the population of S. mutans and an increase of S. sanguis occurred in the plaque. Following the removal of chlorhexidine the population of S. mutans increased again in the presence of sucrose and the number of S. sanguis returned to initial values. When animals were given a sucrose-free diet the low proportion of S. mutans observed following the short-term chlorhexidine period persisted. These data indicate that there is an inverse relationship between the number of S. sanguis and S. mutans in plaque and that the sensitivity in vivo of S. mutans to chlorhexidine can be used to suppress the population of S. mutans with a concomitant rise in the proportion of S. sanguis .     

Evidence for an ecto-ATPase on the cell wall of Streptococcus sanguis

Certain strains of viridans streptococci bind platelets, which release ATP from dense granules and then aggregate. By hydrolyzing the released ATP to the platelet agonist, ADP, cell wall-associated ATPase activity of Streptococcus sanguis may amplify the aggregation of platelets. To identify and characterize this ecto-ATPase activity, whole cells were incubated with [¹⁴C]-ATP. The cell-free nucleotides were separated by thin-layer chromatography and quantified by liquid scintillation counting. Whole-cell activity showed temperature and pH optima in the physiological range. To isolate a soluble fraction with ATPase activity from the cell wall, whole cells were digested under osmotically stable conditions to produce protoplasts. Protoplasts and cells were separated from soluble cell wall materials by centrifugation. ATPase activity in cell fractions was identified by zymograms of native 8% polycrylamide gels after electrophoresis. The ecto-ATPase preparation, membrane and cytoplasmic ATPase in lysed protoplasts showed different zymograms and sensitivity to inhibition by DCCD, ouabain vanadate, azide and NEM. In electron micrographs of ultrathin sections of cells of S. sanguis , ATPase activity was localized to the cell wall. Since the pattern of localization to the wall changed with the phase of growth, the ecto-ATPase of S. sanguis may be associated with the development and maintenance of the cell wall.