Beschreibung:
<jats:title>Summary</jats:title>
<jats:p>The total resistance to a drug shown by a bacterium in a particular medium is defined in terms of the molar drug concentration required to inhibit the rate of growth by 50 per cent. A method of analysis is provided which permits any change in the total resistance to be assigned to either the bacterium (Rfb) or the environment (Rfe) in which the measurement of resistance is made. The application of this analysis to strains of E. coli trained to grow in media containing sulfanilamide showed the following. Strain trained on sulfanilamide in salt-glucose medium. Tested in salt-glucose medium, the increase in resistance was found to be 3-fold against both sulfanilamide and sulfathiazole. The same result was obtained when the strain was tested in peptone medium. Strain trained on sulfanilamide in peptone medium. Tested in salt-glucose medium, the strain showed a 3-fold increase in resistance to both sulfanilamide and sulfathiazole. Tested in peptone medium, however, it showed a 5.6-fold increase to sulfanilamide and a 21-fold increase to sulfathiazole. Strain trained on peptone medium, pH 7.8. Tested in salt-glucose medium, it showed little change in resistance. Tested in peptone medium it showed a 15-fold increase to the sulfanilamide and a 100-fold increase to sulfathiazole. It is concluded that the resistance of the bacterium not only depends upon the medium in which training occurred, but also upon the medium in which the measure of resistance is made. Furthermore, since the development of resistance to sulfanilamide does not always parallel that to sulfathiazole, it appears that the mode of action of these two drugs, though similar, is not identical.</jats:p>