Dental caries is a major medical burden globally, and Streptococcus mutans plays an important role in this pathology by producing acid, thriving in acidic environments, and secreting extensive extracellular polymeric substances (EPS) to form oral biofilms. Periodontitis is another common oral disease affecting the adult population, and dental caries is more prevalent in individuals suffering periodontitis. Xanthine, an intermediate metabolite synthesised during purine metabolism, is used as an oxidative stress or hypoxia stress marker in periodontitis patients, yet its impact on the pathogenesis of dental caries remains unknown. Therefore, this study aimed to investigate the effects of xanthine on S. mutans biofilm lifestyle. Five S. mutans strains (UA-159, R-9, LT-11, NG-8, and GS-5) were used in this study. S. mutans biofilms were developed in 96-well plates, assessed for adhesion (0-90min), biofilm formation (90min- 24h) and biofilm maturation (24h - 48h). There was a significant increase in the biofilm biomass (safranin O assay) in all five strains in the presence of 10 mM xanthine (P0.05). This finding was further supported by scanning electron and confocal microscopic imaging. In the 24h biofilms EPS content, an increase in lactate and proteins detected but not total eDNA (P<0.05). When exposed to <0.1 mM xanthine, there was a significant upregulation of glycosyltransferases (GtfB, GtfC, GtfD) which synthesise extracellular glucans (P<0.05). The results suggest that xanthine stimulates EPS synthesis in S. mutans via upregulating protein secretion and polysaccharide synthesis without affecting the cell numbers. Xanthine may also positively impact on acid synthesis/secretion from S. mutans biofilms. Therefore, findings of this study suggest xanthine encourages S. mutans biofilm formation and virulence, and subsequent risk of dental caries. Effective management of periodontal diseases and conditions with higher oxidative stress is paramount in preventing dental caries.
The role of nucleotide metabolites on the biology of dental plaque
Kou, M. S. L. (Author). 2 Dec 2021
Student thesis: Master's Thesis › Master of Science by Research (MScR)