The tetracyclines, which were discovered in the 1940s, are a family of antibiotics that inhibit protein synthesis by preventing the attachment of aminoacyl-tRNA to the ribosomal acceptor (A) site. Tetracyclines are broad-spectrum agents, exhibiting activity against a wide range of gram-positive and gram-negative bacteria, atypical organisms such as chlamydiae, mycoplasmas, and rickettsiae, and protozoan parasites. Furthermore, in some countries, including the United States, tetracyclines are added at subtherapeutic levels to animal feeds to act as growth promoters.
Tetracycline resistance commonly can be conferred by efflux proteins and ribosomal protection proteins. The genes encoding efflux proteins belong to the major facilitator superfamily (MFS). All the tet efflux genes code for membrane-associated proteins which export tetracycline from the cell. Export of tetracycline reduces the intracellular drug concentration and thus protects the ribosomes within the cell. Efflux genes are found in both gram-positive and gram-negative species. The ribosomal protection proteins have homology to elongation factors EF-Tu and EF-G (259, 292). The greatest homology is seen at the N-terminal area, which contains the GTP-binding domain. Ribosomal protection proteins reduce the susceptibility of ribosomes to the action of tetracyclines.
Here is a list of aminoglycoside resistance types