Chemical Composition and Antibacterial Activity of Essential Oils from Ocimum Species: Potential β-Lactamase Inhibition Revealed by Molecular Docking

Abstract

Aims: This study investigated the chemical composition and antibacterial properties of essential oils from three Ocimum species (O. americanum, O. gratissimum, and O. selloi) and analysed the molecular interactions of their main compounds with β-lactamase. Study Design: This exploratory experimental study integrated laboratory-based in vitro chemical and biological assays with in silico analyses. Place and Duration of Study: All experiments were conducted at the Department of Pharmaceutical Sciences, Federal University of Juiz de Fora (UFJF), Juiz de Fora, Minas Gerais, Brazil, between January 2018 and July 2022. Methodology: The essential oils from O. americanum (EOA), O. gratissimum (EOG), and O. selloi (EOS) were obtained by hydrodistillation and characterised by GC-MS and GC-FID. Antibacterial activity was assessed against S. aureus, S. epidermidis, P. aeruginosa, and E. coli using agar diffusion, followed by determination of minimum inhibitory concentrations (MICs) and minimum bactericidal concentrations (MBCs). Molecular docking was performed to investigate interactions between selected compounds and class A β-lactamase from E. coli. Results: Linalool, 1,8-cineole, and camphor were identified as the major constituents of EOA; eugenol was the major constituent of EOG; and methyl chavicol was the major constituent of EOS. EOS showed no antibacterial activity against the tested species, whereas EOA was effective against S. aureus, with a MIC of 625 µg/mL. EOG exhibited activity against S. aureus, S. epidermidis, and E. coli, with an MIC of 625 µg/mL. Molecular docking analysis indicated that the major identified compounds, namely camphor, cineole, linalool, eugenol, ocimene, and methyl chavicol, may interact with class A β-lactamase from E. coli, suggesting a potential inhibitory effect on this enzyme. Conclusion: Essential oils from O. americanum and O. gratissimum exhibited antibacterial activity, with EOG showing broader activity. Molecular docking revealed interactions with class A β-lactamase, supporting Ocimum oils as promising sources of antibacterial bioactive compounds.