Ferulic acid suppresses Porphyromonas gingivalis biofilm formation via the inhibition of autoinducer-2 production and receptor activity.

Objective: This study aimed to clarify the antibacterial and antibiofilm effects of ferulic acid against periodontal pathogenic bacteria.

Design: The cytotoxicity of ferulic acid was examined using the MTT assay on the human oral epithelial cell line Ca9-22. To determine the minimum inhibitory concentration (MIC) and minimum bactericidal concentration, Porphyromonas gingivalis ATCC 33277, Fusobacterium nucleatum ATCC 25586, Prevotella intermedia ATCC 25611, Aggregatibacter actinomycetemcomitans JP2, and Streptococcus mitis ATCC 903 were treated with ferulic acid. The inhibition of biofilm formation was evaluated by crystal violet staining. The inhibition of P. gingivalis autoinducer-2 (AI-2) production and receptor activity was evaluated by luminescence measurements using the sensor strain Vibrio harveyi BB170.

Results: Ferulic acid did not exhibit any cytotoxicity on human oral epithelial cells. The MICs of ferulic acid against P. gingivalis and A. actinomycetemcomitans were 1000 and 500 µg/mL, respectively. It did not show antibacterial activity against F. nucleatum, P. intermedia, and S. mitis, indicating the weak antibacterial activity of ferulic acid. However, ferulic acid significantly inhibited P. gingivalis biofilm formation at low concentrations below 1/8 MIC. It specifically inhibited AI-2 production from P. gingivalis below 1/8 MIC and suppressed the receptor activity of AI-2.

Conclusions: Although ferulic acid showed weak antibacterial activity against periodontopathogenic bacteria, it had low cytotoxicity and inhibited P. gingivalis biofilm formation. Ferulic acid inhibited AI-2 production and receptor activity, suggesting that ferulic acid is an efficient quorum-sensing inhibitor for controlling P. gingivalis biofilm formation.