Anti-bacterial effect of four extracts from leaves of Dracontomelon dao on Escherichia coli growth using microcalorimetry coupled with principal component analysis

Abstract

The anti-Escherichia coli activities of four extracts in leaves of Dracontomelon dao, a traditional folk herb in China were investigated and compared by microcalorimetry. The four extracts are PE fraction, CHCl3 fraction, EtOAc fraction, and n-BuOH fraction. The heat flow power–time (HFP–time) curves of E. coli growth in the presence of the four extracts were measured using an ampoule method. Then the nine thermal kinetic parameters were obtained from the curves. From the result of principal component analysis, it can be seen that parameters k1, k2, P1, and Qp2 might be the main parameters in evaluating the anti-E. coli effects. In the presence of CHCl3 fraction, EtOAc fraction, and n-BuOH fraction, k2, Qp2 of E. coli decreased with increasing concentrations of the extracts. The EtOAc fraction was observed to have the strongest anti-bacterial activity with half-inhibitory concentration IC50 of 98.5 μg mL−1. So, it can be concluded that EtOAc fraction can be further developed as anti-bacterial bioactive fraction of leaves of Dracontomelon dao.