Divalent cations are able to interact with exopolysaccharides (EPS) and thus are capable to modify the structure and composition of dental biofilm. At the moment, little is known about the adsorption of metals by cariogenic EPS; thus, the aim of the present study was to evaluate the effect of divalent ions (calcium, magnesium, and zinc) on the growth and biofilm formation of mutans streptococci and on the dissolution of hydroxyapatite as well as to investigate their binding to the bacterial EPS. S. mutans strains used in this study show the highest tolerance towards calcium of the ions tested. Growth parameters showed no differences to control condition for both strains up to 100 mM; revealing natural tolerance to higher concentration of calcium in the surroundings. Although excessive levels of calcium did not impair the growth parameters, it also did not have a positive effect on biofilm formation or its binding affinity to EPS. Magnesium-saturated environment proved to be counterproductive as strains were able to dissolve more Ca2+ from the tooth surface in the presence of magnesium, therefore releasing excessive amounts of Ca2+ in the environment and leading to the progression of the disease. Thus, this supports the idea of self-regulation, when more Ca2+ is released, more calcium is bound to the biofilm strengthening its structure and however, also less is left for remineralization. Zinc inhibited bacterial adhesion already at low concentrations and had a strong antibacterial effect on the strains as well as on calcium dissolution; leading to less biofilm and less EPS. Additionally, Zn2+ had almost always the lowest affinity to all EPS; thus, the unbound zinc could also still remain in the surrounding environment and keep its antimicrobial properties. It is important to maintain a stable relationship between calcium, magnesium and zinc as excessive concentrations of one can easily destroy the balance between the three in cariogenic environment and lead to progression of the disease.

中文翻译：

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二价离子对生龋生物膜形成的影响。

二价阳离子能够与胞外多糖 (EPS) 相互作用，因此能够改变牙科生物膜的结构和组成。目前，关于生龋EPS对金属的吸附知之甚少。因此，本研究的目的是评估二价离子（钙、镁和锌）对变形链球菌的生长和生物膜形成以及羟基磷灰石溶解的影响，并研究它们与细菌 EPS 的结合. 本研究中使用的变形链球菌菌株对所测试离子的钙耐受性最高。生长参数显示两种菌株的对照条件均无差异，浓度高达 100 mM；揭示对周围环境中较高浓度钙的天然耐受性。虽然过量的钙不会影响生长参数，它也没有对生物膜形成或其与 EPS 的结合亲和力产生积极影响。镁饱和环境被证明会适得其反，因为在镁存在的情况下，菌株能够从牙齿表面溶解更多的 Ca2+，从而在环境中释放过量的 Ca2+ 并导致疾病的进展。因此，这支持了自我调节的想法，当更多的 Ca2+ 被释放时，更多的钙与生物膜结合，加强其结构，然而，用于再矿化的钙也更少。锌在低浓度下就可以抑制细菌粘附，并且对菌株和钙溶解具有很强的抗菌作用；导致更少的生物膜和更少的EPS。此外，Zn2+ 几乎总是对所有 EPS 的亲和力最低；因此，未结合的锌还可以保留在周围环境中并保持其抗菌特性。保持钙、镁和锌之间稳定的关系很重要，因为其中一种浓度过高很容易破坏生龋环境中三者之间的平衡并导致疾病的进展。