(Mill.) Cav. Aqueous Extract Antibacterial Activity Improved by the Addition of Spenn., Vahl and Benth.

Lavender aqueous extracts are widely used in the Moroccan traditional medicine for their antibacterial properties. However, previous research have generally focused on investigating the antibacterial activity of lavender essential oils. The aim of this study is to evaluate the antibacterial activity of the Moroccan (Mill.) Cav. aqueous extract, alone, as well as in combination with extracts of other plant species known for their antibacterial activity: Spenn., Vahl. and Benth. We have tested the antibacterial activity of , , and aqueous extracts individually and in combination against 34 strains using the agar dilution method. The combination effect was evaluated using the fractional inhibitory concentration (FIC). Polyphenol and tannin contents were determined using Folin-Ciocalteu reagent, and then some phenolic compounds were identified using UHPLC-MS. All the extracts displayed a large spectrum of antibacterial activity, especially against staphylococci, streptococci, and . The minimum inhibitory concentration (MIC) values reached 0.15 ± 0.00 mg/mL for tested with and 0.20 ± 0.07 mg/mL for tested with or . Association of the extract with , and showed synergistic effects (FIC ≤ 1). Moreover, the association of with was active against most of the Gram-negative strains resistant to the individual extracts. Determination of polyphenol and tannin contents showed the richness of the studied plants in these compounds. Additionally, chromatographic analysis demonstrated the high presence of rosmarinic acid in all the studied plant extracts. To our knowledge, this is the first study that shows the enhancing effect of the antibacterial activity of aqueous extract combined with , and . These results confirm the effectiveness of the plant mixtures commonly used by traditional healers in Morocco and suggest that might be used as an antibacterial agent either alone or, more efficiently, in combination with , and .