Water-insoluble exopolysaccharide synthesized by glucosyltransferases mediates the antibacterial activity of ClyR against Streptococcus mutans.

BACKGROUND

Dental caries is a widespread global health issue strongly associated with Streptococcus mutans. Bacteriophage-derived lytic enzymes such as ClyR hold considerable promise as antibacterial potential, but the molecular mechanisms underlying their activity against S. mutans remain unclear.

OBJECTIVE

This study aimed to determine the role of water-insoluble exopolysaccharides (EPS) in mediating the antibacterial activity of ClyR against S. mutans.

DESIGN

We compared the antibacterial effects of ClyR on S. mutans UA159 and its ΔgtfB mutant, which is characterized by reduced synthesis of water-insoluble EPS. Biofilm architecture and susceptibility were assessed using scanning electron microscopy, confocal laser scanning microscopy, and biomass quantification. Adsorption assays were conducted to evaluate the interaction between ClyR and water-insoluble EPS.

RESULTS

The ΔgtfB mutant exhibited significantly higher resistance to ClyR than S. mutans UA159, with reduced biofilm disruption and bacterial loss after treatment. In vitro assays confirmed that water-insoluble EPS specifically adsorbed ClyR, with binding localized to its catalytic PlyCAC domain.

CONCLUSIONS

Water-insoluble EPS synthesized by S. mutans glucosyltransferases plays a critical role in modulating bacterial susceptibility to ClyR. These findings reveal a novel mechanism underlying bacteriophage lysin activity and highlight EPS as a potential target for enhancing ClyR efficacy against cariogenic biofilms.