Microcalorimetric study of the effect of Benzoinum and Styrax on the growth of Escherichia coli

Abstract

In this study, the effects of Benzoinum and Styrax on Escherichia coli (E. coli) growth were investigated by microcalorimetry. Using a TAM Air Isothermal Calorimeter, ampoule method, the power–time curves of E. coli growth at 37°C affected by Benzoinum and Styrax were measured. By analysing some quantitative thermokinetic parameters, such as growth rate constants k, the maximum heat-out power P _m, the time of the maximum heat-out power t _m, the total heat production Q _t and inhibitory ratio I, one could find that low concentrations (0–3.9 mg mL⁻¹) of Benzoinum and Styrax had stimulation effects on E. coli growth, and high concentrations (7.8–125.0 mg mL⁻¹) of these two drugs would inhibit the growth of the bacteria. The antibacterial effects of Benzoinum and Styrax can also be expressed as half inhibitory concentration IC₅₀. The IC₅₀ values for Benzoinum and Styrax are 78.5 and 88.0 mg mL⁻¹, respectively, which suggests that the antibacterial effect of Benzoinum on E. coli was much stronger than that of Styrax. This study provides a useful method to investigate the effects of herbal medicines on microbes. It also supplies some references for the application of Benzoinum and Styrax in clinical treatment.

Keywords:

• Benzoinum
• Styrax
• E. coli
• antibacterial effect
• microcalorimetry

Acknowledgements

We are grateful to the support of National Basic Research Program of China (973 project) (2007CB512606).