Asiatic Acid Disrupts the Biofilm Virulence of Streptococcus mutans by Transcriptional Reprogramming of Quorum Sensing System

Dental caries, a prevalent biofilm-mediated chronic disease, causes enamel demineralization, pulp infection, and systemic complications. Dental plaque biofilm is the initiating factor for the occurrence and development of caries. <i>Streptococcus mutans</i> is an opportunistic pathogen linked to the structure and ecology of dental plaque biofilms. The molecular mechanism of <i>S. mutans</i> during biofilm ontogeny in driving cariogenesis has been extensively elucidated. Here, we observed that asiatic acid is a potent biofilm disruptor that selectively dismantles <i>S. mutans</i> biofilm architectures, prompting us to investigate its mechanism. The minimum biofilm inhibition concentration (MBIC) of asiatic acid on <i>S. mutans</i> was 62.5 μM, but the MBIC level did not substantially impede planktonic growth. Using the static active-attachment model, it was demonstrated that asiatic acid significantly reduced biofilm biomass (<i>p</i> < 0.001) and extracellular polysaccharides (EPS) content (<i>p</i> < 0.001), while concurrently diminishing acid production (<i>p</i> = 0.017) and metabolic activity (<i>p</i> = 0.014). Confocal and scanning electron microscopy further confirmed structural disintegration, including bacterial detachment and reduced biofilm thickness. Transcriptome analysis of <i>S. mutans</i> biofilm treated with asiatic acid revealed 454 differentially expressed genes (adjusted <i>p</i> < 0.05, |log₂FC| ≥ 1). Notably, genes related to the CiaRH two-component system (<i>ciaR</i>, <i>ciaH</i>), a central regulatory hub for biofilm maturation and acid tolerance. This disruption initiates a downstream cascade, causing a coordinated downregulation of critical gene clusters essential for virulence and pathogenesis, including stress response (<i>htrA</i>, <i>clpP</i>, <i>groEL</i>, <i>dnaK</i>), and the glucan-binding protein gene (<i>gbpC</i>) essential for biofilm structural integrity. These findings provide the first mechanistic evidence linking asiatic acid to transcriptional reprogramming in <i>S. mutans</i> biofilm, offering a novel ecological strategy for caries prevention by targeting key regulatory pathways.