tetA

tetA is a gene that encodes a tetracycline efflux transporter that confers resistance to tetracycline antibiotics in bacteria. It is commonly found on plasmids and transposons in Gram-negative bacteria and is one of several tetracycline-resistance determinants, including tetB and tetC. The encoded protein is a membrane-associated efflux pump belonging to the major facilitator superfamily, exporting tetracycline out of the cell using the proton motive force and thereby lowering intracellular drug concentration.

Expression of tetA is typically regulated by a TetR-type repressor that binds an operator region upstream of tetA. In the absence of tetracycline, TetR represses transcription. When tetracycline or related compounds are present, they bind TetR and derepress transcription, leading to the production of the TetA efflux pump and increased resistance.

Genetic context and mobility: tetA is frequently located on conjugative plasmids and linked to mobile elements such as transposons, facilitating horizontal transfer among bacteria. Multiple alleles exist (for example tetA(A), tetA(B), tetA(C)) and may differ in regulatory sequences or substrate range, though they generally confer a similar mechanism of resistance.

Clinical and research relevance: tetA contributes to tetracycline resistance observed in clinical isolates of Escherichia coli, Salmonella, Klebsiella, and other Gram-negative pathogens. Detection is commonly performed by PCR targeting tetA or by phenotypic antimicrobial susceptibility testing. The gene is also used as a selectable marker in molecular cloning in laboratory strains, where tetracycline or related compounds select for transformed cells.