Effects of disinfectants on bacterial metabolism evaluated by microcalorimetric investigations

The technique of microcalorimetry allows uninterrupted observation of the effects of antimicrobial agents on bacterial metabolism; bacteriostasis and bacterial death can be distinguished from one another directly from the thermal output, without the necessity of inactivating the antimicrobial drugs. In contrast to the traditional methods, microcalorimetry assesses the thermal activity of bacteria rather than their multiplication; the microcalorimetrical results correlate with those of traditional test methods as far as MIC (minimal inhibitory concentration) and MBC (minimal bactericidal concentration)_ are concerned. Microcolarimetry permits a clear differentiation between disinfectants and antibiotics/chemotherapeutics, except in the case of polymyxins which, like the tested disinfectants, show a rapid fall to the zero-line of the power-time-curve at bacteridical concentrations. At sub-bactericidal concentrations, however, each of the disinfectants tested produced an individually characteristic microcalorimetrical curve pattern. This leads us to suspect that the various disinfectants attack at different points in bacterial metabolism. Although the technique of microcalorimetry does not replace standard evaluation, it provides additional insight into the mode of action of disinfectants.