# Overexpression of ASvicR combined with the antibacterial monomer DMAHDM interferes with the VicRK two-component system to attenuate the cariogenicity of Streptococcus mutans

## TL;DR

Combining ASvicR overexpression with DMAHDM reduces S. mutans biofilm and acid production, offering a new approach to manage tooth decay.

## Contribution

A novel chemical-genetic strategy combining ASvicR and DMAHDM to interfere with VicRK and reduce cariogenicity in S. mutans.

## Key findings

- Combination treatment reduced biofilm CFU by 4 log units and lowered lactate and EPS levels.
- ASvicR overexpression increased susceptibility to DMAHDM and chlorhexidine by 2-fold.
- In vivo, the treatment reduced caries severity to 12.7% of the control group.

## Abstract

Streptococcus mutans (S. mutans) is a primary cariogenic pathogen responsible for acid production, exopolysaccharides (EPS) production and biofilm formation. Two-component systems (TCS) regulate EPS metabolism, especially the VicRK TCS. Overexpression of antisense vicR (ASvicR) can reduce EPS production and thereby weaken the cariogenicity of S. mutans. Although the antimicrobial monomer dimethylaminohexadecyl methacrylate (DMAHDM) exhibits potent antibacterial properties, mature S. mutans biofilms can protect themselves by extracellular matrix. Emerging evidence suggests that genetic intervention enhances drug efficacy, yet the underlying regulatory mechanisms remain largely unexplored.

To investigate the chemical–genetic cooperative antibiofilm strategy inhibition and mechanisms of ASvicR overexpression combined with DMAHDM on S. mutans biofilm formation, acid and EPS metabolism, and cariogenicity through the VicRK system.

The minimal inhibitory concentration and minimal bactericidal concentration of DMAHDM and chlorhexidine were determined. Biofilm properties were evaluated via biomass assessment, EPS quantification, lactate production measurement, and colony-forming unit counting. Biofilm structures were examined by scanning electron microscopy. Mechanisms were investigated using RT-qPCR, zymography, and western blot. Rat caries model was employed to assess caries formation under different treatment conditions.

The ASvicR strain exhibited an approximate 2-fold increase in susceptibility to DMAHDM and chlorhexidine. The combination treatment reduced biofilm CFU by approximately 4 log units, significantly lowered lactate and EPS levels, and resulted in a loose, porous biofilm structure. The expression levels of cariogenic virulence factors as well as the VicRK TCS genes and proteins were significantly downregulated. In vivo, the combined treatment reduced the overall caries severity score to 12.7% of the control group (p<0.05) without observing any systemic adverse effects.

The strategy of combining ASvicR overexpression with DMAHDM effectively modulates EPS metabolism and cariogenicity in S. mutans by interfering with the VicRK TCS, providing a potential therapeutic approach for clinical caries management.