Comparison of Tetracycline and Minocycline Transport in Escherichia Coli

Differences between minocycline and tetracycline transport were demonstrated in an Escherichia coli strain with and without an R factor (R46) which confers moderate Tc resistance. Minocycline uptake was similar in R(+) and R(-) organisms, whereas tetracycline uptake was decreased in the R(+) as compared to the R(-) organism. Sodium azide had little effect on tetracycline uptake by either strain but minocycline uptake was completely inhibited by azide. p-Chloromercuribenzoate greatly decreased tetracycline uptake in both strains while minocycline uptake was markedly augmented. Both minocycline and tetracycline were effective inducers of decreased tetracycline transport, but only tetracycline had an effect on minocycline uptake. Mutual inhibition of uptake of one antibiotic by the other could not be demonstrated. These studies indicate different mechanisms of transport of minocycline and tetracycline in E. coli.