Enterococci are largely commensal organisms that are opportunistic pathogens. Underlying disease, an immunocompromised state, age, lengthy hospital stays or long-term care, invasive treatments, and prior antimicrobial therapy - or any combination thereof - are factors that are associated with significant infections with these species.
As noted previously, enterococci are intrinsically resistant to many antibiotics. Intrinsic resistance affects not only beta-lactams (including a broad range of cephalosporins) and aminoglycosides but also clindamycin and trimethoprim/sulfamethoxazole. The standard recommended therapy for systemic infections is a combination of either penicillin or vancomycin and an aminoglycoside (gentamicin or streptomycin). The goal of combination therapy is to achieve a synergistic bactericidal effect between the cell wall agent and the aminoglycoside. The Clinical and Laboratory Standards Institute (CLSI) contraindicates reporting any of these drugs as susceptible because these interpretations will not predict in vivo response.
In recent decades, increasing resistance to other antibiotics through acquired resistance mechanisms has become a growing therapeutic and infection control problem. Of key concern are high-level resistance (HLR) to aminoglycosides and increasing resistance to glycopeptides such as vancomycin.
