Bioactive constituents with antibacterial, resistance modulation, anti-biofilm formation and efflux pump inhibition properties from Aidia genipiflora stem bark

Abstract

Background Antimicrobial resistance is a global health challenge. The involvement of bacterial biofilms and efflux pumps in the development of multidrug resistance (MDR) is well established. Medicinal plants have been proposed as alternatives for combating MDR focusing on their bioactive constituents with resistance modulatory activities. This study was aimed at investigating the stem bark of Aidia genipiflora for bioactive constituents with anti-biofilm, efflux pump inhibition and resistance modulatory activities. Method The crude methanol extract was purified by column chromatography and isolated compounds characterized by mass and nuclear magnetic resonance spectrometry. Antibacterial activity was determined by the High-throughput spot culture growth inhibition and the broth micro-dilution assay. The ethidium bromide accumulation assay was used to determine efflux pump inhibition property. Biofilm inhibition was determined in a microplate crystal violet retention assay. Results Purification of the ethyl acetate fraction led to the isolation of oleanonic acid ( 1 ), 4-hydroxy cinnamic acid docosyl ester ( 2 ), β-stigmasterol/β-sitosterol (mixture 3a/b ) and D-mannitol ( 4 ). The minimum inhibitory concentrations (MICs) ranged from 250 to >\u2009500\u2009μg/mL for extracts and fractions and from 15 to 250\u2009μg/mL for compounds. In the presence of sub-inhibitory concentrations of the compounds, the MIC of amoxicillin against E. coli (20\u2009μg/mL) and P. aeruginosa (320\u2009μg/mL) was reduced by 32 and 10 folds respectively. The whole extract demonstrated anti-biofilm formation and efflux pump inhibition in E. coli , S. aureus and P. aeruginosa . The sterol mixture ( 3a/b ) at concentration of 100\u2009μg/mL caused the highest inhibition (73%) of biofilm formation in S. aureus . Oleanonic acid ( 1 ) demonstrated remarkable efflux pump inhibition at MIC of 7.8\u2009μg/mL in E. coli better than the standard drugs verapamil and chlorpromazine. Conclusion This study confirms the prospects of A. genipiflora as a source of new antibacterial agents and adjuvants that could interact with some resistance mechanisms in bacteria to enhance the activity of hitherto ineffective antibiotics. “ A small portion of the study has been presented in a conference in the form of poster ”.