The adaptation of Bact. lactis aerogenes to varying concentrations of an antibacterial drug (proflavine)

Abstract

Previous work indicated that when bacteria become adapted to resist the action of drugs an adjustment of enzyme balance occurs, and that there should be a quantitative relation between the degree of adjustment and the conc. of the drug which provokes the "training." Theoretical equations are given connecting the lag (minimal with respect to age) of a given strain of cells, tested at various drug concs., with the steady conc. established in the cell of an essential metabolite, whose synthesis the drug impairs. In this way the effect of training at various drug concs. can be predicted. Exptl. curves have been detd. showing the relation between lag and proflavine conc. for strains of Bact. lactis aerogenes (Aerobacter aerogenes) trained respectively to a series of increasing concs. of the drug. These curves form a family, the spacing of which is directly related to the conc. at which training occurred. They are adequately described by the equations. One conclusion from the results is that the conc. c of the intermediate metabolite is at first reduced by an amt. directly proportional to the proflavine conc., and that subsequent adaptation restores c to precisely its normal level. The simple behavior holds over a considerable range of drug cones. (0-200 mg./l.) but appears to break down at very high concs. (to which, although with more difficulty, the cells are still adaptable).