Microcalorimetry coupled with principal component analysis for investigating the anti-Staphylococcus aureus effects of different extracted fractions from Dracontomelon dao

With the prevalence resistance of Staphylococcus aureus to antibacterial agents, developing novel antibacterial agents is urgent. Recently, plant extracts have got more focus. In this study, the power-time curves produced by S. aureus under the action of the four extracted fractions (PE, CHCl3, EtOAc, and n-BuOH fractions) from the leaves of Dracontomelon dao were determined by microcalorimetry, and then some quantitative parameters, such as growth rate constant k, total heat output Q t, maximum heat-output power P m, and the appearance time t m were obtained. By analyzing the parameters using principal component analysis, the anti-S. aureus effects of the four fractions were systematically evaluated and compared. Meanwhile, the total flavonoid contents in these fractions were analyzed. The results have evidenced that different fractions using various extraction solvents expressed various anti-S. aureus effects, and the inhibitory effects were presented in a flavonoid content-dependent manner. The EtOAc fraction with the highest total flavonoid content (41.86 %) expressed the strongest anti-S. aureus effect with half-inhibitory concentration (IC50) of 83.93 μg mL−1, which might be applied as a novel antibacterial agent in practice for some infectious diseases. In addition, the microcalorimetric method should be strongly suggested in screening for novel antibacterial agents for fighting against pathogenic bacteria.