Enterococci: Susceptibility patterns and therapeutic options

Enterococci do not possess the common virulence factors found in many other bacteria, but they have a number of other characteristics which make them particularly pathogenic. These organisms are intrinsically resistant to a number of antimicrobial agents, including beta-lactams (penicillins and cephalosporins), polymyxins and the lincosamides. They are also tolerant to the bactericidal activity of penicillins and glycopeptides, and some of the group have acquired resistance to a number of other clinically important antimicrobial agents including ampicillin, aminoglycosides, chloramphenicol and erythromycin. Numerous national and international studies have demonstrated the changes in the antibiotic- resistance of enterococci. Many strains now exhibit multiple drug resistance, the most important being high-level resistance to streptomycin and gentamicin. Organisms exhibiting this high-level resistance are usually resistant to all synergistic combinations of beta-lactam antibiotics and aminoglycosides. Ampicillin-resistant strains are now emerging, some of which are beta-lactamase producers. While resistance to glycopeptides remains rare, it is increasing dramatically in many areas of the world. As nosocomial isolates of enterococci have displayed resistance to essentially every useful antimicrobial agent, it is likely to become increasingly difficult to treat and control enterococcal infections. The glycopeptide antibiotics vancomycin and, particularly, teicoplanin are the only alternatives currently available. Although a bactericidal combination of antibiotics appears necessary only in endocarditis and meningitis and although knowledge of the prevalence of resistant strains can be used to guide the selection of appropriate therapy, optimal regimens for the treatment of infections caused by multiresistant strains have yet to be determined. In vitro synergy studies on the combination of ciprofloxacin and teicoplanin indicate promising activity against high-level resistant enterococci. Therapeutic experience with animal models, however, is necessary to assess the likely value of this combination in treating human infection.