Application of microcalorimetry and principal component analysis

A useful microcalorimetric technique based on the bacterial heat production was applied to evaluate the antibacterial effects of Benzoinum and Styrax on the growth of Staphylococcus aureus (S. aureus). The thermogenic power-time curves of S. aureus growth in the presence of the two drugs were determined by a thermal activity monitor (TAM) air isothermal microcalorimeter, ampoule mode, at 310 K. Some quantitative metabolic parameters, such as growth rate constant k, the heat-flow power P, the appearance time for the heat power t, and the heat production Q were obtained from these curves. By analyzing these curves and some quantitative parameters using principal component analysis (PCA), the antibacterial effects of Benzoinum and Styrax on S. aureus growth were accurately evaluated from the change of the two main parameters, the heat-flow power for the second peaks P (2nd) and total heat production Q (t): the antibacterial effects of the two drugs at concentrations of 0-125 mg mL(-1) were both enhanced with increasing the concentration, and Benzoinum with IC50 of 132.2 mg mL(-1) had stronger antibacterial effect than Styrax with IC50 of 179.8 mg mL(-1). This study provides some useful references for the application of Benzoinum and Styra as potential antibacterial agents. Microcalorimetry is a powerful analytical tool for the characterization of the microbial growth progress and the evaluation of the drugs' efficiency.