GC-MS characterization of bioactive compounds from Lippia multiflora Moldenke (Verbenaceae) flower essential oils and their antibiofilm potential against resistant bacteria

Bacterial resistance to antibiotics is a global health challenge, partly due to biofilm formation, which protects bacteria against drugs and the immune system. This study investigated the potential of essential oils from Lippia multiflora flowers to inhibit bacterial biofilms, offering a natural alternative to address bacterial resistance. Antibacterial activity against Staphylococcus aureus and Streptococcus mutans was assessed using the agar diffusion method on Luria Bertani agar. The minimal inhibitory concentration (MIC) was determined using the serial liquid dilution process and the minimal bactericidal concentration (MBC) by the bacterial growth assay on Luria Bertani agar. Biofilm inhibition was tested spectrophotometically at 590 nm using the crystal violet assay, antioxidant activity was performed using the DPPH method, and phytochemical composition was determined by gaz chromatography-mass spectrometry (GC-MS) analysis. The essential oils produced larger inhibition zones against S. aureus (28.38 ± 0.23 mm) and S. mutans (24.5 ± 0.25 mm) compared with standard antibiotics (gentamicin disc, 13.5 ± 0.07 mm for S. aureus; oleandomycin disc, 16.5 ± 0.05 mm for S. mutans). MIC was ranged from 0.10 ± 0.00% for both S. aureus and S. mutans, and MBC was not achieved within the tested range (≤ 0.10%). The essential oils inhibited biofilm formation more effectively than salicylic acid (p < 0.001), with inhibition rates of 59.97 ± 0.68% for S. aureus and 71.63 ± 0.15% for S. mutans. Essential oils showed stronger antioxidant activity (DPPH IC₅₀ value of 0.23 ± 0.02 µg/µL) compared with the ascorbic acid (DPPH IC₅₀ value of 0.33 ± 0.01 µg/µL). GC-MS analysis identified 22 terpenes, including major components β-caryophyllene (43.55%), germacrene D (16.44%), elemol (10.33%) and eucalyptol (6.41%). These results demonstrated that the essential oils of L. multiflora flowers are a potent source of antibacterial compounds.