Identification of the active position is the first step in the exploration of medical herbs. The effects of four Vitex negundo Linn extracts: n-hexane extracts, chloroform extracts, ethyl acetate extracts, and methanol extracts on Escherichia coli (E. coli) were investigated by microcalorimetry. The methanol extracts displayed strongest influence on the thermogenic growth curves of E. coli. The ethyl acetate extracts displayed lower influence than the methanol extracts. The n-hexane extracts and chloroform extracts displayed no obvious influence. The growth rate constants of E. coli and inhibition ratio under the actions of methanol and ethyl acetate extracts were calculated. Their inhibitory effects increased with concentrations.

Key words: E. coli, active position, inhibition, microcalorimetry, Vitex negundo