Development and characterisation of a novel antimicrobial peptide GA-C16G2 targeting Streptococcus mutans.

OBJECTIVES: This study aimed to develop a Streptococcus mutans (S. mutans)-targeted peptide for caries management and evaluate its antibacterial efficacy.

METHODS: A novel peptide, GA-C16G2, was synthesised by attaching gallic acid (GA) onto an S. mutans-targeted antimicrobial peptide, C16G2. Peptide purity and stability were measured using high-performance liquid chromatography (HPLC). The secondary structure of GA-C16G2 was assessed using circular dichroism (CD) spectroscopy, and cytotoxicity was evaluated with the PrestoBlue assay. Antimicrobial activity against oral bacterial species was determined using minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) assays. Time-kill and biofilm inhibition assays further characterised the peptide's activity. Bacterial morphology and biofilm structure were analysed by transmission electron microscopy (TEM) and scanning electron microscopy (SEM).

RESULTS: GA-C16G2 was synthesised with 95.02 % purity, and its secondary structure closely resembled that of the parent peptide C16G2. GA-C16G2 exhibited good stability in artificial saliva and showed low cytotoxicity towards human gingival fibroblasts. GA-C16G2 demonstrated potent antimicrobial activity against S. mutans (MIC: 3.1 μM, MBC: 20.8 μM) while showing weaker effects against commensal bacterial species. A time-kill assay confirmed the rapid bactericidal activity of GA-C16G2, reducing S. mutans viability by 97.22 % within one minute. GA-C16G2 also inhibited S. mutans biofilm formation. TEM and SEM images confirmed bacterial and biofilm disruption.

CONCLUSION: This study demonstrates the successful development of a biocompatible and stable peptide, GA-C16G2, with rapid and potent selective in vitro antimicrobial activity against S. mutans.

CLINICAL SIGNIFICANCE: GA-C16G2 offers a novel therapeutic approach for targeted prevention and treatment of dental caries.