[Bacterial resistance mechanisms for tetracyclines].

Tetracycline resistance mechanism is unique in bacterial resistance mechanisms because of being mainly based on the drug efflux except for the ribosomal protection mechanism in some tetracycline-resistant Gram-positive bacteria. Tetracycline efflux proteins such as Tet(B) and Tet(C) of Gram-negative bacteria are estimated to have 12-membrane-spanning structure common to the major facilitator family transporters. We experimentally proved the 12-membrane-spanning structure of Tet(B) by site-directed chemical labeling. On the other hand, the tetracycline efflux proteins such as Tet(K) and Tet(L) of Gram-positive bacteria are estimated to have 14-membrane-spanning structure. We first presented the experimental evidence for the 14-spanning structure of Tet(K) based on the Tet(K)-PhoA fusion protein analysis. Another mechanism of tetracycline resistance is a ribosomal protection encoded by tet(M) and let(O). These genes encode the elongation factor(EF-Tu or EF-G)-like protein, whereas the molecular mechanism of the resistance has not yet been revealed.