Antibiotic therapy in 1994: mechanisms of resistance.

Drug-resistant organisms are appearing with increasing frequency. Of particular concern are drug-resistant strains of enterococci, streptococci, and pneumococci. Bacteria use several adaptive mechanisms to thwart the actions of antimicrobials, including enzymes, alterations in cell membrane permeability, export of antibiotics from the cell, alteration of molecular structures, and transfer of resistance to other species. Countering the effects of resistance requires judicious use of antibiotic therapy and a clear understanding of the biologic mechanisms involved.