Microcalorimetric investigation of the effect of berberine alkaloids from Coptis chinensis Franch on Staphylococcus aureus growth

The inhibitory effects of three berberine alkaloids (BAs) from rhizome of Coptis chinensis Franch, a traditional Chinese medicinal (TCM) herb, on Staphylococcus aureus growth were investigated by mi- crocalorimetry. The power–time curves of S. aureus with and without BAs were acquired; meanwhile the extent and duration of inhibitory effects on the metabolism were evaluated by studying the growth rate constant (k), half inhibitory ratio (IC50), maximum heat-output power (Pmax), peak time of maximum heat-output power (tp) and total heat production (Qt). The value of k of S. aureus in the presence of the three BAs decreased with the increasing concentrations of BAs. Moreover, Pmax was reduced and the value of tp increased with increasing concentrations of the three drugs. The inhibitory activity varied with different drugs. The values of IC50 of the three BAs are respectively, 101.4 μg/mL for berberine, 241.0 μg/mL for palmatine and 792.3 μg/mL for jateorrhizine. The sequence of antimicrobial activity of the three BAs is: berberine > palmatine > jateorrhizine. It is suggested that the functional group me- thylenedioxy or methoxyl at C2 on the phenyl ring could possibly improve antimicrobial activity more strongly than hydroxyl at C2 on the phenyl ring.