Geraniol attenuates Streptococcus mutans biofilm and virulence as an anti-caries agent

Streptococcus mutans-induced dental caries is largely mediated by robust biofilm formation, making it notoriously difficult to treat with conventional antimicrobials. To overcome the limited efficacy and penetration challenges associated with current conventional treatments, this study investigated the in vitro and in silico effects of geraniol on S. mutans biofilm and the expression of genes associated with biofilm formation. Antibacterial activity was evaluated using disk diffusion and minimum inhibitory concentration (MIC) assays. Membrane integrity, anti-biofilm activity, and structural alterations were assessed through intracellular protein and nucleic acid leakage analyses, biofilm eradication assays, and scanning electron microscopy (SEM), respectively. Quantitative real-time PCR (qRT-PCR) was used to analyze the expression of biofilm-associated genes. Molecular docking was performed to investigate interactions between geraniol and major S. mutans biofilm -related proteins. Geraniol exhibited marked antibacterial activity against S. mutans isolates, with inhibition zone diameters of 12.0 ± 0.0 mm and a MIC value of 107 µg/mL. Treatment induced significant leakage of intracellular proteins and nucleic acids, indicating disruption of membrane integrity. Exposure to 4×MIC markedly impaired mature biofilm architecture. SEM analysis confirmed severe morphological damage, including membrane disruption and cellular deformation. qRT-PCR analysis demonstrated significant downregulation of the biofilm-associated genes gtfB, gtfC, and gtfD following treatment with geraniol. Molecular docking further revealed stable interactions between geraniol and key biofilm regulatory proteins, including GtfB, GtfC, and GtfD. These findings highlight the ability of pure geraniol to dismantle both the structural integrity and genetic machinery of the bacteria, supporting its potential as a novel therapeutic candidate against biofilm-mediated oral infections.