RESISTANCE OF ESCHERICHIA COLI TO TETRACYCLINES

Abstract

A strain of Escherichia coli, highly resistant to chlortetracycline and partially cross-resistant to tetracycline, was isolated. The nitro-reductase system of the resistant cells was inhibited to a smaller extent by chlortetracycline than was the corresponding enzyme of sensitive cells. The incorporation of leucine in-vitro into the ribosomal protein of cell-free preparations from sensitive and resistant cells was equally inhibited by chlortetracycline. Resistant cells accumulated less chlortetracycline and tetracycline than did sensitive cells when both were cultured in the presence of these drugs. The uptake of tetracycline by both sensitive and resistant E. coli was dependent on the presence of glucose in the medium. Fractionation of cells cultured in medium containing [C14]chlortetracycline indicated that the largest proportion of radioactivity in sensitive cells was in the fraction consisting mainly of cell-wall material. There was no Concentration of radioactivity in any 1 fraction of the resistant cells. No evidence was obtained for a specific tetracycline -excretion system in the resistant cells. The significance of these results in relation to current theories of the antibiotic action of and resistance to the tetracycline drugs is discussed.