Antibiotic resistance in Gram-positive cocci

Gram-positive cocci still predominate as a cause of nosocomial- and communi ty-acquired infections. These organisms frequently reveal a high natural, i ntrinsic resistance to antimicrobials. Additionally, these bacteria are abl e to acquire resistance to frequently used drugs rapidly through selective pressure of the environment and via the genetic evolution of bacteria. The wide application of antimicrobials in medical and veterinary practice, usag e of antibiotics in agriculture and common usage of antiseptics and disinfe ctants result in selective pressure. The use of antibiotics directly select s resistant variants to different antibiotics or disinfectants. The same ge netic element (e.g. qac or smr) conferring resistance to some disinfectants are often present on the same plasmid conferring resistance to antibiotics . Selection of resistant variants occurs most frequently in the hospital en vironment. Staphylococcus aureus and enterococci are the most commonly isol ated bacteria causing nosocomial infections. Among those giving therapeutic problems are methicillin-resistant staphylococci and vancomycin-resistant enterococci. Resistance to high levels of aminoglycosides or penicillins am ong hospital enterococcal strains can completely abolish synergism of the d rugs. In these cases glycopeptides will be the drugs of choice in the treat ment of serious infections. Recently S. aureus strains with decreased susce ptibility to vancomycin has appeared. A mechanism for this elevated resista nce, although intensively investigated, still remains unknown. (C) 2000 Els evier Science B.V. and International Society of Chemotherapy. All rights re served.