Investigation of antibacterial activity of two kinds of novel schiff bases on Escherichia coli by microcalorimetry

The microcalorimetric method was used to study the antibacterial activity of two newly synthesized Schiff base compounds (H₂L ^3′ and H₂L³) on Escherichia coli, trying to obtain the action on both of multiplying bacteria and non-multiplying bacteria at one experiment. The metabolic power-time curves of the bacteria treated with the compounds were obtained, and the thermokinetic parameters were analyzed, from which the antibacterial activities of these compounds were evaluated. The results showed that both of the two compounds have good activity on aerobic multiplying metabolism of E. coli, with the value of IC₅₀ 75.8 and 168.8 mg/L respectively, but have not effective action on fermentation metabolism of E. coli. The action of the compounds on the non-multiplying metabolism was investigated by taking the heat output of E. coli in the stationary phase as the guideline of the activity. The value of MSC₅₀ (minimum stationary-cidal concentration 50) of them is 118 and 187.5 mg/L, respectively. So, H₂L^3′ has stronger antibacterial action on E. coli than H₂L³ either for multiplying bacteria or non-multiplying bacteria, and their activity on the aerobic multiplying bacteria of E. coli is mainly shown. It does strongly suggest that the calorimetric method should play an important role in the fight against the drug-resistant bacteria.