Calorimetric investigation of the effect of hydroxyanthraquinones in Rheum officinale Baill on Staphylococcus aureus growth

The inhibitory effects of five hydroxyanthraquinones (HAQs) from root and rhizoma of Rheum officinale Baill, a traditional Chinese medicinal (TCM) herb, on Staphylococcus aureus growth were investigated by calorimetry. The power-time curves of S.aureus with and without HAQ were acquired and the extent and duration of inhibitory effects on the metabolism evaluated by growth rate constants (k1, k2), half inhibitory ratio (IC50), maximum heat output (Pmax) and peak time (tp). The value of k1 and k2 of S. aureus in the presence of the five HAQs decreased with the increasing concentrations of HAQs. Moreover, Pmax was reduced and the value of tp increased with increasing concentrations of the five drugs. The inhibitory activity varied for different drugs. IC50 of the five HAQs was 4 μg ml−1 for emodin, 3.5 μg ml−1 for rhein, 10 μg ml−1 for aloe-emodin, 1000 μg ml−1 for chrysophanol, 1600 μg ml−1 for physcion. The sequence of antimicrobial activity of the five HAQs: rhein > emodin > aloe-emodin > chrysophanol > physicion.