A potent dual-targeting antimicrobial peptide specifically against Streptococcus mutans biofilms.

INTRODUCTION

Dental caries, which are caused primarily by Streptococcus mutans biofilms, demand targeted antimicrobial strategies to overcome the limitations of broad-spectrum agents such as chlorhexidine (CHX). Here, we designed and synthesized a chimeric peptide (PMF) integrating three functional domains to achieve species-selective anti-microbial and anti-biofilm activities.

METHODS

The antimicrobial peptides were chemically synthesized, and their biological activities were assessed. These included hemolytic and cytotoxic effects, antibacterial activity against planktonic bacteria, and antibiofilm properties. Antibacterial activity against planktonic bacteria was determined by MIC, MBC, time‑kill kinetics, and live/dead staining. Antibiofilm properties were evaluated by biofilm imaging, post‑antibiofilm effect, and crystal violet quantification. We further investigated their mechanisms of action, focusing on membrane disruption via nucleotide leakage, PI uptake, and zeta potential measurements. The damage to biofilms was also examined by assessing membrane potential and using scanning electron microscopy.

RESULTS

PMF exhibited potent efficacy against S. mutans (MIC/MBC = 1.56/3.13 μM) while sparing commensals (S. sanguinis/S. gordonii MIC >100 μM). At 25 μM, a 15 min treatment inhibited 4 h biofilm growth without affecting commensal growth. Time-killing assays demonstrated the superiority of PMF over CHX. For 24 h biofilms, PMF outperforms CHX in terms of destruction efficiency and suppresses biofilm formation at sub-MIC doses. Mechanistic studies revealed that PMF employs electrostatic interactions to bind bacterial membrane lipids, which compromises membrane integrity and causes nucleic acid leakage in planktonic bacteria. For biofilm bacteria, PMF induced membrane depolarization and disrupted EPS, exposing embedded bacteria and leading to their lysis.

CONCLUSIONS

This dual-targeting peptide achieves precise S. mutans elimination while maintaining microecological balance.

CLINICAL SIGNIFICANCE: This work offers a promising translational framework for next-generation anti-caries therapies, enabling targeted and effective prevention and treatment approaches in clinical settings.