Evaluation of silibinin as an efflux pump inhibitor in Bacillus subtilis

Abstract

Antibiotic resistance has become a global health problem for humankind. Improper use of antibiotics resulted in the increasing evolved bacterial resistance to them. There are different types of bacterial resistance mechanisms including efflux pumps. To overcome the efflux pump activity on the drugs, combinatorial therapy of the existing antimicrobials with natural products is a promising insight to prevent increasing multidrug resistance. In this study, the inhibitory action of a plant-derived molecule silibinin on efflux pumps of Bacillus subtilis was investigated. The cellular effect of silibinin was investigated using minimum inhibitory concentration and growth studies. In addition, the efflux pump action of silibinin was monitored by ethidium bromide accumulation assay on the organism. According to results, silibinin has a MIC value between 100-200 µgmL-1 on microplate assay and 100 µgmL-1 of silibinin inhibited the cell growth. Ethidium bromide accumulation assays were performed at a safe silibinin range (25 and 50 µgmL-1) for eliminating the cell death, and ethidium bromide accumulation was increased with the increasing silibinin concentration. Ethidium bromide accumulation and growth results proved that silibinin has significant efflux pump inhibitor activity on Bacillus subtilis cells and silibinin is a promising inhibitor candidate to eliminate bacterial resistance mechanism.