Dashper S G, Reynolds E C
Biochemistry and Molecular Biology Unit, School of Dental Science, The University of Melbourne, Australia.
J Dent Res. 2000 Jan;79(1):90-6. doi: 10.1177/00220345000790011601.
Oral streptococci produce large quantities of organic acids as the end-products of carbohydrate fermentation. In an approach to determine if oral streptococci exhibit differential sensitivities to organic acid anions, we determined the effects of formate, lactate, and acetate on intracellular pH maintenance, glycolysis, and growth of Streptococcus mutans and Streptococcus sanguis. Growth was determined as maximum culture optical density in the presence of the organic acid anions at pH 7.1, 6.7, 6.3, and 6.1, and the effects of the anions on glycolytic activity and intracellular pH were determined at pH 7.0 and 5.0. At pH 7.1, the organic acid anions had little effect on growth of either species. At the lower pH values, all of the anions reduced the maximum culture optical density of both species in a pH- and concentration-dependent manner, with S. sanguis being more sensitive to growth inhibition than S. mutans. The organic acid anions had little or no effect on glycolytic activity of either species at pH 7.0. However, all of the organic acid anions tested reduced glycolytic activity at pH 5.0 in a concentration-dependent manner, with S. sanguis being more sensitive than S. mutans. The inhibition of glycolysis could be related to the pKa of the organic acid, with formate and lactate being more inhibitory than acetate. The organic acid anions decreased the intracellular pH of S. mutans and S. sanguis, glycolyzing at an extracellular pH of 5.0, such that the reduction in glycolytic activity caused by the organic acid anions could be directly attributed to the fall in intracellular pH. In conclusion, the production of lactic acid in plaque would not only lower pH, thereby having a disadvantageous effect on less aciduric oral streptococci, such as S. sanguis, but would also increase their sensitivity to the effects of low pH, helping S. mutans to become more dominant.
口腔链球菌在碳水化合物发酵过程中会产生大量有机酸作为终产物。为了确定口腔链球菌对有机酸阴离子是否表现出不同的敏感性，我们测定了甲酸盐、乳酸盐和乙酸盐对变形链球菌和血链球菌细胞内pH维持、糖酵解及生长的影响。在pH 7.1、6.7、6.3和6.1条件下，于有机酸阴离子存在时测定生长情况，以最大培养物光密度表示，同时在pH 7.0和5.0条件下测定阴离子对糖酵解活性及细胞内pH的影响。在pH 7.1时，有机酸阴离子对两种菌的生长几乎没有影响。在较低pH值时，所有阴离子均以pH和浓度依赖的方式降低了两种菌的最大培养物光密度，血链球菌比变形链球菌对生长抑制更敏感。在pH 7.0时，有机酸阴离子对两种菌的糖酵解活性几乎没有影响。然而，在pH 5.0时，所有测试的有机酸阴离子均以浓度依赖的方式降低了糖酵解活性，血链球菌比变形链球菌更敏感。糖酵解的抑制可能与有机酸的pKa有关，甲酸盐和乳酸盐的抑制作用比乙酸盐更强。在细胞外pH为5.0进行糖酵解时，有机酸阴离子降低了变形链球菌和血链球菌的细胞内pH，因此有机酸阴离子引起的糖酵解活性降低可直接归因于细胞内pH的下降。总之，菌斑中乳酸的产生不仅会降低pH，从而对耐酸性较弱的口腔链球菌（如血链球菌）产生不利影响，还会增加它们对低pH影响的敏感性，有助于变形链球菌变得更加占优势。
