Resistance to tetracycline by an active tetracycline efflux. This is an energy-dependent process that decreases the accumulation of the antibiotic in whole cells. This protein functions as a metal-tetracycline/H(+) antiporter. This protein is used as a marker in many commonly used cloning vectors, such as pBR322 and pACYC184. Belongs to the major facilitator superfamily. TCR/Tet family.