Abstract
Microbial infections remain a public health problem due to the upsurge of bacterial resistance. In this study, the antibacterial, antibiofilm, and efflux pump inhibitory activities of the stem bark of Acacia macrostachya, an indigenous African medicinal plant, were investigated. In traditional medicine, the plant is used in the treatment of microbial infections and inflammatory conditions. A crude methanol extract obtained by Soxhlet extraction was partitioned by column chromatography to obtain the petroleum ether, ethyl acetate, and methanol fractions. Antibacterial, efflux pump inhibition and antibiofilm formation activities were assessed by the high-throughput spot culture growth inhibition (HT-SPOTi), ethidium bromide accumulation, and the crystal violet retention assay, respectively. The minimum inhibitory concentrations (MICs) of the crude extract and major fractions ranged from 250 to ≥500 μg/mL. At a concentration of 3.9–250 μg/mL, all extracts demonstrated >80% inhibition of biofilm formation in S. aureus. In P. aeruginosa, the EtOAc fraction showed the highest antibiofilm activity (59–69%) while the pet-ether fraction was most active against E. coli biofilms (45–67%). Among the test samples, the crude extract, methanol, and ethyl acetate fractions showed remarkable efflux pump inhibition in S. aureus, E. coli, and P. aeruginosa. At ½ MIC, the methanol fraction demonstrated significant accumulation of EtBr in E. coli having superior efflux inhibition over the standard EPIs: chlorpromazine and verapamil. Tannins, flavonoids, triterpenoids, phytosterols, coumarins, and saponins were identified in preliminary phytochemical studies. Stigmasterol was identified in the EtOAc fraction. This study justifies the use of A. macrostachya in the treatment of infections in traditional medicine and highlights its potential as a source of bioactive compounds that could possibly interact with some resistance mechanisms in bacteria to combat antimicrobial resistance.
Highlights
Antimicrobial resistance (AMR) is a global menace that has jeopardised the effective prevention and treatment of infectious diseases [1]
Previous studies report that plant extracts and secondary metabolites have the potential to counteract certain resistance mechanisms in bacteria to successfully restore the antibacterial effect of hitherto ineffective antibiotics [5, 6]
Biofilm Inhibition Assay. e effect of the crude extract and fractions on biofilm formation by S. aureus, E. coli, and P. aeruginosa was investigated using the microplate crystal violet stain retention method previously described by Abidi et al and the method description partly reproduces their wording [23]
Summary
Antimicrobial resistance (AMR) is a global menace that has jeopardised the effective prevention and treatment of infectious diseases [1]. High levels of drug resistance have been exhibited mainly through the expulsion of antibiotics by membrane-based polypeptides called efflux pumps [2] as well as the development of biofilms that protect them from antimicrobial agents [3]. Previous studies report that plant extracts and secondary metabolites have the potential to counteract certain resistance mechanisms in bacteria to successfully restore the antibacterial effect of hitherto ineffective antibiotics [5, 6]. The roots, stem bark, and leaves are used for the treatment of oral infections including dental caries and gingivitis [7, 8]. In a continuing effort to investigate the bioactivities of tropical medicinal plants [17, 18], the antibacterial, antibiofilm, and efflux pump inhibition activities of the stem of A. macrostachya (Leguminoseae) were studied
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