A microcalorimetric technique based on bacterial heat-output was explored to evaluate the toxic effect of different diphenol species on the growth of Escherichia coli (E. coli). Power-time curves of the growth metabolism for E. coli in the presence of different diphenol species were studied using a multi-channel microcalorimetric system with an ampoule method at 37 degrees C. The growth rate constant (k), generation time (t(G)), inhibitory ratio (I), half-inhibitory concentration (IC(50)) and the total thermal effect (Q(T)) for E. coli were obtained. The results show that catechol and hydroquinone are more toxic to E. coli than resorcinol. In all cases, the growth rate constants of E. coli (in log phase) decreased as the concentrations of these diphenols increased. Among these diphenols species, catechol was found to be the most poisonous species at an IC(50) of 323.5 micro g/mL against E. coli. Hydroquinone exhibited moderate virulence with an IC(50) of 1196 micro g/mL and resorcinol had the lowest toxicity with an IC(50) of 2113 micro g/mL. The microcalorimetric bioassay can be a quantitative, inexpensive, and versatile method for acute cellular toxicity study.
A microcalorimetric technique based on bacterial heat output was explored to evaluate the toxic effect of iron species on Escherichia coli. Power-time curves of the growth metabolism of E. coli and the effect of different iron species on it were studied using the TAM III multichannel microcalorimetric system, isothermal mode, at 37 degrees C. The differences in shape of the power-time curves and the thermodynamic and kinetic characteristics of E. coli growth have been compared. The thermodynamic parameters, that is, growth rate constant (k), inhibitory ratio (I), half-inhibitory concentration (IC(50)), P(max), and Q(total), have been calculated. The experimental results reveal that the sequence of antibiotic activity of the different iron species (three forms) on E. coli growth is Fe(3+) (ferric citrate) > Fe(2+) (ferrous chloride) > Fe(3+) (ferric chloride). These results are important to further studies of the physiology and pharmacology of iron species as antibacterial agents.
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