On the nature of tetracycline resistance in Bacillus subtilis mediated by the plasmid pT 127

The nature of tetracycline resistance was studied in a strain of Bacillus subtilis carrying the plasmid pT 127 in comparison with the parental strain. The resistance has been shown to be inducible in both strains upon exposure to subinhibitory concentrations of tetracycline. No modification of the protein-synthesizing activity of the ribosomes or intracellular inactivation of the antibiotic was observed in both strains. Accumulation of labeled tetracycline in B. subtilis was found to be particularly low in the wild-type strain, compared to other bacterial species, with concentration gradients of only 2 to 3 fold. From the kinetics obtained it is likely that the permeation of the antibiotic does not correspond to an active process in B. subtilis. A fairly good correlation was established between the level of resistance obtained after induction or by the presence of the plasmid pT 127 and a decrease in the binding capacity of the cell for the antibiotic.