LC-Q-Orbitrap HRMS Profiling and Functional Characterization of Ocimum basilicum var. purpureum Extract as an Ampicillin-Modulating Agent against Escherichia coli
Abstract
Abstract Plant-derived polyphenol-rich extracts are of interest as resistance-modifying agents because they may affect bacterial redox balance, membrane-associated bioenergetics, and antibiotic susceptibility. In this study, the antibiotic-modulatory potential of Ocimum basilicum var. purpureum ethanol extract (OBEE) was investigated against Escherichia coli NM111, a katG::lacZ reporter strain derived from E. coli K-12. The phytochemical composition by LC-Q-Orbitrap HRMS analysis tentatively annotated 102 phytochemical constituents in OBEE. Hydroxycinnamic acids and their derivatives formed the most numerous group (32 compounds), including a series of caffeic-acid oligomers and salvianolic-type depsides, followed by flavonoids (29 compounds). The extract was dominated by caffeic-acid–derived metabolites, principally rosmarinic acid, chicoric acid, sagerinic acid, salvianolic acid K and caftaric acid, together with quercetin, luteolin and cyanidin derivatives. OBEE showed high total phenolic content (317.75 ± 4.11 µg GAE mg⁻¹) and strong DPPH radical-scavenging activity, with an IC₅₀ of 19.37 ± 0.38 µg mL⁻¹, close to that of catechin, with rosmarinic acid identified as the dominant antioxidant compound. Although OBEE did not exhibit direct antibacterial activity against E. coli NM111 up to 2 mg mL⁻¹, it potentiated ampicillin at non-inhibitory concentrations, reducing the ampicillin MIC two-fold (modulation factor ≥ 2) and showing synergistic interaction (FICI katG::lacZ…
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