Evaluation of in vitro antibacterial activity and phytochemical profile of aqueous leaf extract of Asystasia variabilis

This study evaluated the in vitro antibacterial effect and the phytochemical profile of aqueous extract of fresh mature leaves of Asystasia variabilis, a Sri Lankan indigenous plant, against four common wound infective bacteria (Staphylococcus aureus, Bacillus subtilis, Pseudomonas aeruginosa and Escherichia coli) using Kirby-Bauer disk diffusion test. Gentamicin 10 μg/ disk and distilled water was used as positive and negative controls respectively The study revealed, for the first time, that the extract possessed significant antibacterial activity against all four test organisms in a concentration dependent manner (r values ranging from 0.921-0.992, P<0.01) with inhibition zone diameters ranging between 8 and 28 mm. Highest antibacterial activity was exhibited against B. subtilis at 1000 μg/ disk (27.43-+0.02 mm). The extract showed inhibitory effects comparable to gentamicin towards B. subtilis and P. aeruginosa at 500 μg/ disk and towards E. coli and S. aureus at 1000 μg/ disk. Qualitative phytochemical screening revealed the presence of flavonoids, tannins, phenols, cardiac glycosides, amino acids, carbohydrates, alkaloids and saponins. Therefore it is likely that the antibacterial effect of the extract is mediated by synergistic mechanisms. Furthermore, results of this study scientifically justified the claim traditional and folk medicine in the treatment of abscesses, wounds and ulcers and indicated the potential for the development of a novel drug from mature leaves of Asystasia variabilis.