A stage-like appearance occurred in the first exponential phase of several bacteria's thermogenic curves determined by a microcalorimetry ampoule method, and the growth rate constants of these stages were very different, which has not been found before in a stop-flow method and disturbs the precise antibacterial activity evaluation. In order to find the possible reasons, the growth of E. coli under different environmental atmosphere as well as the condition similar to the stop-flow method was determined and analyzed. The environmental atmosphere is mainly responsible for this variation. A criterion was recommended for the selection of growth rate constant under various atmosphere when determined by ampoule method.

Key words: microcalorimetry, ampoule method, E. coli, growth rate constant, environmental atmosphere