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Treatment of enterococcal infections

Barbara E Murray, MD
Section Editor
Daniel J Sexton, MD
Deputy Editor
Elinor L Baron, MD, DTMH


Enterococcal species can cause a variety of infections, including urinary tract infections, bacteremia, endocarditis, and meningitis. The antimicrobial agents available for treatment of enterococcal infection are reviewed here, followed by treatment approaches for clinical syndromes caused by enterococci. Other issues related to enterococci are discussed in detail separately. (See "Mechanisms of antibiotic resistance in enterococci" and "Epidemiology, prevention, and control of vancomycin-resistant enterococci" and "Microbiology of enterococci".)

Infections due to Enterococcus faecalis tend to be more virulent than infections due to Enterococcus faecium. In addition, bacteremia due to E. faecalis is more likely to be associated with endocarditis than bacteremia due to E. faecium. Clinical isolates of E. faecalis tend to be considerably more susceptible to beta-lactam agents than clinical isolates of E. faecium. Isolates of E. faecalis are typically susceptible to ampicillin but resistant to quinupristin-dalfopristin, whereas most E. faecium isolates are resistant to ampicillin (minimum inhibitory concentration ≥16 mcg/mL) but susceptible to quinupristin-dalfopristin.


Approach to susceptible strains — Enterococci are relatively resistant to penicillin and ampicillin (compared with most streptococci); even when these cell wall–active agents inhibit enterococci, they often do not kill them; vancomycin is even less bactericidal. E. faecium clinical isolates are more resistant to penicillin than E. faecalis (minimum inhibitory concentration for 90 percent of strains [MIC90] >16 mg/mL versus 2 to 4 mcg/mL, respectively); MICs of ampicillin are usually 1 dilution lower than those of penicillin. Piperacillin activity is similar to that of penicillin, and imipenem generally is active against penicillin-susceptible E. faecalis. Cell wall–active agents with limited or no activity against enterococci include nafcillin, oxacillin, ticarcillin, ertapenem, most cephalosporins, and aztreonam.

Enterococci are also relatively impermeable to aminoglycosides, and the serum concentrations of aminoglycosides required for bactericidal activity are much higher than can be achieved safely in humans. However, the simultaneous use of a cell wall–active agent raises the permeability of the cell so that an intracellular bactericidal aminoglycoside concentration can be achieved [1]. Bactericidal antimicrobial activity is warranted in clinical circumstances of life-threatening infection. (See 'Approach to specific infections' below.)

Enterococcal isolates are usually tested for susceptibility to ampicillin, penicillin, and vancomycin. The presence of beta-lactamase is very rare; it confers resistance to penicillin and ampicillin when large numbers of organisms are present (such as in the setting of a valvular vegetation), even though the organism may test susceptible using standard laboratory inocula. Thus, to rule out this possibility in patients with life-threatening enterococcal infection (such as meningitis or endocarditis), some experts recommend that the isolate be screened for beta-lactamase production with nitrocefin, a chromogenic cephalosporin, even if ampicillin susceptible. There are also rare reports of more highly penicillin- and/or imipenem-resistant isolates of E. faecalis with retained ampicillin susceptibility (albeit with higher-than-usual MICs) [2,3]; this has been associated with specific amino acid changes in the low-affinity penicillin-binding protein (PBP) of E. faecalis.

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Literature review current through: Nov 2017. | This topic last updated: Jul 06, 2017.
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