Exploring the In Vitro Antibacterial Properties of Milicia regia and Entandrophragma angolensis: Insight Into Their Antibiofilm and Efflux Pump Inhibitory Activities

Abstract

Introduction: Biofilms are breeding grounds for adapted and acquired antibiotic resistance through increased efflux activities and horizontal gene transfer. Medicinal plants are sources of antimicrobial agents for the treatment of bacterial, parasitic, and fungal infections. Aim: In this research, we examined antimicrobial, antibiofilm, and efflux pump inhibition activity of the methanolic extracts of the stem barks of Milicia regia and Entandrophragma angolensis. Methods: Crude methanolic extracts were assessed using three distinct assays: the high-throughput spot culture growth inhibition (HT-SPOTi) assay for bacterial growth inhibition, a crystal violet–based antibiofilm screening assay to quantify their biofilm‑inhibitory activity and the ethidium bromide accumulation assay for evaluating changes in bacterial cell membrane permeability against Mycobacterium smegmatis, Mycobacterium aurum, Staphylococcus aureus, and Pseudomonas aeruginosa. Results: The preliminary qualitative phytochemical screening suggested the presence of tannins, flavonoids, terpenoids, glycosides, alkaloids, and saponins. The minimum inhibitory concentrations for extracts against S. aureus, P. aeruginosa, M. aurum, and M. smegmatis were 250, 125, 500, and 250 μg/mL, respectively, and for E. angolensis: 125, 125, 500, and 500 μg/mL, respectively. Both plants displayed significant (∗∗∗ρ < 0.005) biofilm inhibition activities against all bacteria with the highest inhibition recorded in S. aureus: M. regia, E. angolensis, and the reference drug ciprofloxacin were 73%, 62%, and 79%, respectively. Conclusion: The extracts produced marked antiefflux pump effects against S.aureus and P. aeruginosa. This study established the antibacterial, antibiofilm, and efflux pump inhibitory capacities of M. regia and E. angolensis and provides the rationale for their folkloric uses in the treatment of infections.