Microcalorimetric Studies of the Action on Four Organic Acids in Radix Isatidis on the Growth of Microorganisms

The actions of four organic acids in Radix Isatidis, a traditional Chinese medicinal (TCM) herb, on Escherichia coli, Staphylococcus aureus, and Shigella dysenteriae growth were investigated by microcalorimetry. The power-time curves of Escherichia coli, Staphylococcus aureus, and Shigella dysenteriae with and without organic acids were acquired. Meanwhile, the extent and duration of the inhibitory effects on the metabolism were evaluated by growth rate constants (k1, k2), maximum heat output (Pm), and peak time (tp). The inhibitory activity varied with different drugs. The order of anti-microbial activity of the four organic acids on Escherichia coli, Staphylococcus aureus, and Shigella dysenteriae was: syringic acid > 2-amino-benzoic acid > salicylic acid > benzoic acid. Benzoic acid promoted the growth of Staphylococcus aureus and Shigella dysenteriae. This study provided a basis for further researches on Radix Isatidis