Enterococci are gram-positive, facultative anaerobic organisms. Enterococcus faecalis and E. faecium cause a variety of infections, including endocarditis, UTI, prostatitis, intra-abdominal infection, cellulitis, and wound infection as well as concurrent bacteremia.
Enterococci are part of the normal intestinal flora. They used to be classified as group D streptococci but are now considered a separate genus. There are > 17 species, but E. faecalis and E. faecium most commonly cause infections in humans.
Enterococci typically cause
(See also the American Heart Association's Infective Endocarditis in Adults: Diagnosis, Antimicrobial Therapy, and Management of Complications.)
Enterococci associated with endocarditis are difficult to eradicate unless a combination of certain cell wall–active drugs (eg, penicillin, ampicillin, amoxicillin, piperacillin, vancomycin) plus an aminoglycoside (eg, gentamicin, streptomycin) is used to achieve bactericidal activity. However, some cell wall-active drugs have limited or no activity against enterococci; they include nafcillin, oxacillin, ticarcillin, ertapenem, most cephalosporins, and aztreonam. E. faecium are more resistant to penicillin than E. faecalis. When an aminoglycoside cannot be used, the combination of penicillin or ampicillin plus ceftriaxone is an effective alternative for the treatment of E. faecalis endocarditis. Imipenem and, to a lesser degree, meropenem are active against E. faecalis.
For complicated skin infections due to vancomycin-susceptible enterococci, daptomycin, linezolid, tedizolid, and tigecycline are effective treatment options.
Piperacillin-tazobactam and imipenem or meropenem are recommended for complicated intra-abdominal infections when enterococci are known or presumed to be involved.
UTIs do not require bactericidal therapy and, if the causative organism is sensitive, are usually treated with a single antibiotic such as ampicillin. Nitrofurantoin and fosfomycin are often effective against vancomycin-resistant enterococcal UTI.
In the past several decades, resistance to multiple antimicrobial drugs has increased rapidly, especially among E. faecium.
Resistance to aminoglycosides (eg, gentamicin, streptomycin), particularly with E. faecium, continues to emerge.
Vancomycin-resistant enterococci (VRE) may also be resistant to other glycopeptides (eg, teicoplanin), aminoglycosides, and cell wall–active beta-lactams (eg, penicillin G, ampicillin). When identified, infected patients are strictly isolated. Recommended treatment includes streptogramins (quinupristin/dalfopristin for E. faecium only) and oxazolidinones (linezolid, tedizolid). Daptomycin and tigecycline have in vitro activity against VRE and may be off-label treatment options.
Beta-lactamase–producing enterococci are occasionally encountered, particularly when large numbers of organisms are present (eg, in endocarditis vegetation). Resistance may be present clinically even though the organism appears susceptible based on standard testing. Vancomycin or combination beta-lactam/beta-lactamase inhibitor antibiotics (eg, piperacillin/tazobactam, ampicillin/sulbactam) can be used.