The Bacteriostatic Actions of Tetracycline and Oxytetracycline

Abstract

The bacteriostatic actions of tetracycline and oxytetracycline on cultures of A. aerogenes in glucose-mineral salt media have been studied. Both antibiotics show two modes of action, one of which is non-operative under aerobic conditions and is ascribed to an interference with the disposal of hydrogen in unaerated cultures. The other mode of action can be accounted for by an interference with the synthesis of protein. Quantitative measurements of the dependence of the degree of inhibition on the pH and the concentration of magnesium ions are in accord with attributing inhibitory power solely to the non-ionic molecular forms of the antibiotics. The possible contributions of the two modes of action to the cytotoxic action are discussed.