Enterococcal infections. Resistance mechanisms, treatment strategies, and hospital issues

Long recognized as an occasional cause of urinary tract infection or endocarditis, in recent years the enterococcus has become a significant hospital-associated pathogen. Common infections related to this organism include urinary tract infections, wound and intraabdominal infections, and bacteremia. Perhaps the greatest significance of this organism relates to its inherent resistance to several antimicrobials and its propensity to acquire resistance to others. Traditional antimicrobial resistance issues include relative resistance to β-lactam antibiotics, resistance to low concentrations of aminoglycosides, and tolerance to agents which interfere with cell wall formation (β-lactams and vancomycin). Emerging resistance problems include high-level resistance to aminoglycoside antibiotics and the rapid increase in vancomycin-resistant enterococci (VRE) which has occurred over the past decade. Unique genetic mechanisms have been described to account for these new resistance patterns. In general there is not clear evidence that VRE are any more virulent than susceptible enterococci, but the special issues and limitations they raise in terms of antibiotic choices make infection due to VRE more complex to manage. VRE can spread within health care institutions and may result in infection or gastrointestinal colonization with these organisms. Infection control policies, including isolation, strict hand washing, and barrier protection require considerable attention. The majority of infections other than endocarditis caused by susceptible strains of enterococci (e.g., urinary tract infections) should respond to bacteriostatic therapy, particularly when the patient has normal immune defenses. Endocarditis should be treated with bactericidal regimens, if any are feasible. Treatment of infections due to VRE, especially those due to Enterococcus faecium, are a continuing challenge because such isolates are usually resistant to multiple agents. Novel regimens of both established and experimental antimicrobial therapy have been used and are currently under study. For these reasons we recommend that it is best to approach treatment of serious infections due to multiresistant strains with the assistance of someone knowledgeable in the field.