Thermo-chemical investigation on the quantity-antibacterial effect relationship of five berberine alkaloids in Rhizoma Coptidis on Escherichia coli growth

The inhibitory effects of five berberine alkaloids from rhizoma of Rhizoma Coptidis, a traditional Chinese medicinal herb, on Escherichia coli growth were investigated at 37 °C by microcalorimetry. The five alkaloids were: berberine, coptisine, epiberberine, palmatine and jatrorrhizine. The thermogenic power-time curves of Escherichia coli growth with and without berberine alkaloids were by the Thermal Activity Monitor (TAM) Air Isothermal Calorimeter, meanwhile the values of growth rate constants k, growth inhibitory ratio I, maximum heat output Pm and generation time tG were calculated. In accordance with thermo-kinetic model, the relationships of the drugs, such as I - c, k - c, Pm - k were investigated. c was the concentration of the drugs. Half-inbibitory concentration of the drugs, IC50, was obtained by quantitative analysis. From the view of thermo-kinetics and molecular structure, the relationship between quantity and effects of five berberine alkaloids was discussed. Also, the minimum inhibitory concentration (MIC) and the minimal bacteriocidal concentration (MBC) of the five berberine alkaloids on anti-Escherichia coli growth was obtained by tube dilution method. Meanwhile, the action mechanism of antibacterial effect was studied. The efficiency of these five berberine alkaloids on anti-growth of E. coli was as follows: berberine > coptisine > epiberberine > palmatine > jatrorrhizine. This work illustrated that microcalorimetry was a useful tool to investigate the antibacrerial activity of medicinal herbs and provided a general model to study the quantity and antimicrobial effects relationship of medicinal herbs from the view of thermo-chemistry and molecular structure.