Targeted isolation of phenolic compounds from Halia Bentong (Zingiber officinale Roscoe var. Bentong) and their antibacterial activities against Porphyromonas gingivalis

• Halia Bentong phenolics show bactericidal activity against P. gingivalis. • 6-Gingerol and 6-shogaol suppress fimA and rgpA gene expression. • TEM reveals altered structures in P. gingivalis treated with phenolics. • Halia Bentong phenolics reduce fimbriae expression and adhesion. • Halia Bentong-derived phenolics show potential as antimicrobial agents. Porphyromonas gingivalis is a keystone pathogen associated with chronic periodontitis. This study evaluated the antibacterial activities of the major pungent compounds 6-gingerol and 6-shogaol, derived from Halia Bentong, against P. gingivalis . Both compounds were isolated from Halia Bentong and characterised through thin-layer chromatography (TLC), high-performance liquid chromatography (HPLC), ultraviolet-visible spectroscopy (UV–Vis) and liquid chromatography time-of-flight mass spectrometry (LC-MS). The preliminary qualitative antibacterial activities of both compounds were evaluated using agar well diffusion. The broth microdilution method determined the minimum inhibitory concentration (MIC), minimum bactericidal concentration (MBC) and half-maximal inhibitory concentration (IC 50 ) values. The expression levels of fimA and rgpA virulence genes were assessed by quantitative reverse transcription polymerase chain reaction (RT-qPCR) after treatment with both compounds at 0.5 × MIC. Changes in the morphology of P. gingivalis induced by both compounds were investigated using transmission electron microscopy (TEM). Agar well diffusion exhibited inhibition zones of 14.63 ± 1.49 mm for 6-gingerol and 19.38 ± 2.81 mm for 6-shogaol. The broth microdilution method revealed that 6-gingerol had MIC and MBC values of 5 mg/mL and an IC₅₀ of 2.3 mg/mL, while 6-shogaol exhibited MIC and MBC values of 10 mg/mL and an IC₅₀ of 5.9 mg/mL. Significant downregulation of fimA and rgpA in P. gingivalis was observed after treatment with both compounds ( p < 0.05). TEM analysis revealed low fimbriae expression on the cell surface. Total cell shrinkage was observed at 1.0 × MIC of 6-gingerol-treated cells. In addition, a protruding bulge was observed in 6-shogaol-treated P. gingivalis at 1.0 × MIC, potentially leading to cell death. 6-Gingerol and 6-shogaol have potential as alternative antibacterial agents to control P. gingivalis infections.