General mechanisms of antimicrobial resistance.

Bacteria can become resistant to antimicrobial agents by two routes, either by mutation or by the inheritance of new genetic information in the form of resistance plasmids. The mechanisms by which bacteria express resistance are manyfold, and five different biochemical mechanisms have been demonstrated in clinical isolates. The most important mechanisms are alteration of the drug target site, interference with the transport of the antimicrobial agent into the cell, and detoxification (inactivation) of the drug in the immediate environment of the cell.