Two transport systems for tetracycline in sensitive Escherichia coli: critical role for an initial rapid uptake system insensitive to energy inhibitors.

Escherichia coli sensitivity to tetracycline involves transport and accumulation of the antibiotic within the cell by two different uptake systems: an initial rapid uptake, which occurs over the initial 6 min of contact of the cell with tetracycline, and a slower uptake system, which continues indefinitely and whose rate of uptake is 1/10 that of the rapid system. Only the slow uptake system is blocked by inhibitors of energy-driven systems; it appears to be particularly dependent upon energy from oxidative phosphorylation. Although both uptake systems lead to accumulation of intracellular tetracycline and contribute to the cell's sensitivity, the rapid uptake system appears to be the more important. While these studies confirm active transport of tetracycline into the cell, they demonstrate that a critical uptake system which appears insensitive to metabolic inhibitors occurs initially.