Abstract
BackgroundDivalent 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.ResultsS. 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.ConclusionIt 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.
Highlights
Divalent cations are able to interact with exopolysaccharides (EPS) and are capable to modify the structure and composition of dental biofilm
The aim of the present study was to evaluate the effect of divalent ions 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
The growth rate of S. mutans clinical isolate (CI) was affected only when glucose and CaCl2 were present; all other combinations showed no significant decrease in this parameter
Summary
Divalent cations are able to interact with exopolysaccharides (EPS) and are capable to modify the structure and composition of dental biofilm. Steiger et al BMC Microbiology (2020) 20:287 demineralization of the hard tissues of the teeth [1,2,3, 8, 9] This manifestation occurs only if there is an imbalance between the protective and the pathogenic factors inside the oral biofilm. Decisive parts of the matrix in the dental biofilm are the extracellular polysaccharides (EPS), which in caries lesions are predominantly produced by S. mutans [17]. The development of EPS depends on various factors such as pH, temperature, time, and the composition of the medium, in which the sources of carbon, nitrogen, and divalent ions play an important role [18]. Since EPS contains negative charged functional groups and has the potential in removing heavy metal ions from solutions, there is the possibility that divalent ions can bind EPS as well and change its whole structure and function [19]
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