van der Mei H C, de Soet J J, de Graaff J, Rouxhet P G, Busscher H J
Laboratory for Materia Technica, University of Groningen, The Netherlands.
Caries Res. 1991;25(6):415-23. doi: 10.1159/000261404.
Mutans streptococci comprise a group of seven closely related, yet distinct species. The distinction between the four species used in this study, namely Streptococcus sobrinus, Streptococcus cricetus, Streptococcus rattus, and Streptococcus mutans, has been made only recently on the basis of DNA homologies. In order to determine if there is a difference in the physicochemical surface properties of these species, strains were characterized by contact angles, zeta potentials and isoelectric points (IEP), elemental surface compositions by X-ray photoelectron spectroscopy, and molecular moieties by infrared spectroscopy. Contact angles, particularly when measured with water, can be considered a measure of cell surface hydrophobicity; zeta potentials reflect the charge of the outermost cell surface; X-ray photoelectron spectroscopy yields the relative abundance of carbon, oxygen, nitrogen, and phosphorus over the outer 5 nm of the bacterial cell surface; infrared spectroscopy enables a molecular characterization in terms of proteins, phosphates, and polysaccharides. All four species were homogeneous with regard to their physicochemical surface properties. However, the S. rattus species were clearly different from the others on the basis of the low water contact angle (21 +/- 2 vs. 26-31 degrees), highly negative zeta potential and lack of IEP, and high oxygen/carbon (0.50 +/- 0.02 vs. 0.41-0.43) and phosphorus/carbon (0.016 +/- 0.001 vs. 0.006-0.008) surface concentration ratios. Amongst the other differences observed, each species had a characteristic pH dependence of their zeta potential measured in phosphate buffer, yielding an IEP of 1.7, 2.1, and 2.5 for S. cricetus, S. sobrinus, and S. mutans, respectively. However, a cluster analysis on the zeta potential data showed only an isolated cluster for the S. rattus species. Thus it is likely that the higher cariogenicity of S. sobrinus with respect to S. cricetus and S. mutans is, in addition to a higher acidogenicity, due to the smaller negative surface charge, giving an increased adhesion to negatively charged tooth surfaces. S. rattus is expected to be the least adherent strain in the oral cavity as it carries a relatively high negative surface charge.
变形链球菌由七个密切相关但又不同的物种组成。本研究中使用的四个物种，即远缘链球菌、仓鼠链球菌、大鼠链球菌和变形链球菌，直到最近才根据DNA同源性得以区分。为了确定这些物种的物理化学表面性质是否存在差异，通过接触角、zeta电位和等电点（IEP）对菌株进行了表征，通过X射线光电子能谱确定了元素表面组成，通过红外光谱确定了分子部分。接触角，特别是用水测量时，可被视为细胞表面疏水性的一种度量；zeta电位反映了最外层细胞表面的电荷；X射线光电子能谱得出细菌细胞表面外层5纳米内碳、氧、氮和磷的相对丰度；红外光谱能够从蛋白质、磷酸盐和多糖方面进行分子表征。所有四个物种在其物理化学表面性质方面都是均匀的。然而，大鼠链球菌物种在低水接触角（21±2度对26 - 31度）、高度负的zeta电位和缺乏等电点以及高氧/碳（0.50±0.02对0.41 - 0.43）和磷/碳（0.016±0.001对0.006 - 0.008）表面浓度比的基础上，明显与其他物种不同。在观察到的其他差异中，每个物种在磷酸盐缓冲液中测量的zeta电位都有特征性的pH依赖性，仓鼠链球菌、远缘链球菌和变形链球菌的等电点分别为1.7、2.1和2.5。然而，对zeta电位数据的聚类分析仅显示大鼠链球菌物种为一个孤立的聚类。因此，除了更高的产酸性外，远缘链球菌相对于仓鼠链球菌和变形链球菌更高的致龋性可能是由于其较小的负表面电荷，从而增加了对带负电荷牙齿表面的粘附。由于大鼠链球菌携带相对较高的负表面电荷，预计它是口腔中粘附性最低的菌株。
