Antibacterial and Antibiofilm Activity of Lavandula angustifolia Essential Oil for Inhibiting Primary Biofilm Colonizers: An In Vitro Study

Objective: The present study aimed to assess the effectiveness of Lavandula angustifolia (L. angustifolia) essential oil (EO) in inhibiting bacterial growth and biofilm formation of primary colonizers, such as Streptococcus sanguinis (S. Sanguinis), Streptococcus mitis (S. mitis), and Streptococcus oralis (S. oralis), in an in vitro setting. Methods: Gas chromatography-mass spectrometry (GC–MS) analysis was used to examine the oil extracted from L. angustifolia EO by hydrodistillation. Agar well diffusion and broth dilution techniques were performed to evaluate antibacterial activity and Minimum Inhibitory Concentrations (MICs) and Minimum Bactericidal Concentrations (MBCs), respectively, against the three American Type Culture Collection (ATCC) strains. In contrast, the qualitative tube method was performed to assess the antibiofilm effect. Chlorhexidine 0.12% was used as a positive control, and all experiments were performed in triplicate (n = 3). Data were analyzed using SPSS (version 26), with p ≤ 0.05 considered statistically significant. Results: GC–MS identified 25 constituents in L. angustifolia EO, with linalool (20.99%) predominant. The EO (5–20%) showed dose-dependent antibacterial activity, producing inhibition zones up to 16.2 mm compared with 16–18 mm for chlorhexidine. MIC/MBC values (µL/mL) were 1.56/3.125 for S. mitis, 0.39/0.781 for S. oralis, and 0.156/3.12 for S. sanguinis. For the mixed-species consortium, MIC and MBC were 0.156 and 3.12 µL/mL, respectively. The EO demonstrated moderate to weak antibiofilm activity. Conclusions: L. angustifolia EO showed concentration-dependent antibacterial activity against primary oral colonizers. While chlorhexidine 0.12% produced larger inhibition zones overall, L. angustifolia EO at higher concentrations, especially 15%, demonstrated comparable efficacy against S. mitis. These findings suggest its potential as a supplementary therapeutic natural adjunct for preventing early plaque formation.