[Paper Review] Evaluation of in vitro antibacterial activity and phytochemical profile of aqueous leaf extract of Asystasia variabilis

R Wijerathna, Nav Asanthi+3 more|ArXiv.org|Aug 26, 2025

Essential Oils and Antimicrobial Activity3 citations

TL;DR

The study evaluates in vitro antibacterial activity and phytochemical profile of aqueous leaf extract from Asystasia variabilis against four wound-infective bacteria using Kirby-Bauer diffusion, showing concentration-dependent inhibition and notable activity compared with gentamicin for some strains.

ABSTRACT

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.

Motivation & Objective

• Motivate exploration of traditional Sri Lankan plant Asystasia variabilis for wound infection treatment.
• Assess the in vitro antibacterial activity of the plant's aqueous leaf extract against four bacteria.
• Profile the phytochemical constituents of the extract.
• Compare antibacterial efficacy with a standard antibiotic control.
• Discuss potential for drug development from mature leaves.

Proposed method

• Prepare aqueous extract from fresh mature leaves of Asystasia variabilis.
• Assess antibacterial activity using Kirby-Bauer disk diffusion with four bacteria.
• Test organisms: Staphylococcus aureus, Bacillus subtilis, Pseudomonas aeruginosa, Escherichia coli.
• Use gentamicin 10 μg/disk as positive control and distilled water as negative control.
• Measure inhibition zone diameters (mm) and assess concentration dependence (r values).
• Perform qualitative phytochemical screening for flavonoids, tannins, phenols, cardiac glycosides, amino acids, carbohydrates, alkaloids, and saponins.

Experimental results

Research questions

• RQ1 Does the aqueous leaf extract exhibit in vitro antibacterial activity against S. aureus, B. subtilis, P. aeruginosa, and E. coli?
• RQ2 Is the antibacterial activity concentration-dependent, and how does it compare to gentamicin?
• RQ3 Which phytochemicals are present in the extract that might mediate antibacterial effects?
• RQ4 Can the extract support potential development of new treatments for abscesses, wounds, and ulcers?

Key findings

• The extract showed significant antibacterial activity against all four test organisms.
• There is a concentration-dependent inhibition with r values between 0.921 and 0.992 (P<0.01).
• Inhibition zone diameters ranged from 8 to 28 mm across conditions.
• Highest activity was against B. subtilis at 1000 μg/disk with 27.43 ± 0.02 mm.
• The extract's activity was comparable to gentamicin for B. subtilis and P. aeruginosa at 500 μg/disk and for 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, suggesting possible synergistic antibacterial mechanisms.