Antibacterial effect of different extracts from Wikstroemia indica on Escherichia coli based on microcalorimetry coupled with agar dilution method

Abstract

The root of Wikstroemia indica has been widely used in China as folk medicine for the treatment for arthritis, whooping cough, cancer, and bacillosis. However, the constituents which have antibacterial activity were not clarified yet. In this study, the antibacterial effect of five extracts from W. indica on Escherichia coli was evaluated by microcalorimetry coupled with agar dilution method. The ethanol extract of W. indica was isolated with organic solvents of different polarities including petroleum (P.E.) extract, chloroform (CHCl3) extract, ethyl acetate (EtOAc) extract, n-butylalcohol (nBuOH) extract, and residue extract. The metabolic profiles of E. coli growth at 37 °C were measured by microcalorimetry. According to the principal component analysis, k1, k2, and P1 were obtained from heat flow power–time (HFP–time) curve. The agar dilution method was performed to verify the results of thermodynamics. The results of microcalorimetric experiment indicated that EtOAc fraction demonstrated the strongest antibacterial activity with half-inhibitory concentration of 92.4 μg mL−1. Meanwhile, similar results were gained from the common method of agar diffusion, which suggested that EtOAc extract could be further developed as antibacterial bioactive fraction of W. indica. Altogether, microcalorimetry is a useful technique to provide sufficient quantitative information and evaluate the antimicrobial effect with its sensitive.