In vitro antimicrobial potential of extracts and phytoconstituents from Gymnema sylvestre R.Br. leaves and their biosafety evaluation

The in vitro antimicrobial screening of Gymnema sylvestre leaves against 13 test pathogens established its broad spectrum activity with average inhibition zone ranging from 14 to 23 mm. The antimicrobial activity of the classically- optimized aqueous extract was enhanced up to 1.45 folds, when subjected to statistical optimization using Response Surface Methodology (RSM) and was thermostable. Ethyl acetate was found to be the best organic extractant with Klebsiella pneumoniae 1 (31.5 mm) and Staphylococcus epidermidis (25.5 mm) being the most sensitive among Gram negative and Gram positive bacteria, respectively. Among the major group of phytoconstituents detected, tannins were the most abundant followed by flavonoids and phytosterols, while triterpenes were absent. Flavonoids and cardiac glycosides exhibited a broad range of antimicrobial potential, with inhibition zone ranging from 13 to 35 mm, where Candida albicans was the most sensitive organism. Ethyl acetate extract showed better potency with lowest Minimum inhibitory concentration (0.1–1 mg ml(−1)) than the aqueous extract (1–3 mg ml(−1)) and all partially purified phytoconstituents (0.1–10 mg ml(−1)). The ethyl acetate extract and flavonoids were highly potent, as they exhibited a total activity potency ranging from 41.4 to 1045 ml g(−1). Time kill studies revealed their microbicidal action, where ethyl acetate extract had a kill time from 0 to 12 h. However, among phytoconstituents, flavonoids were the most effective (0–8 h). The MIC and time kill study was also compared to that of standard antibiotics. These findings indicate that Gymnema sylvestre can be a potential source for development of leading metabolites against pathogens of clinical importance like Pseudomonas aeruginosa, Candida albicans, Escherichia coli, Staphylococcus aureus etc. They were neither mutagenic nor cytotoxic, as revealed by Ames and MTT assay. ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (doi:10.1186/s13568-017-0416-z) contains supplementary material, which is available to authorized users.