What is the difference in treatment approach for Enterococcus faecium vs Enterococcus faecalis infections?

Treatment Differences Between Enterococcus faecium and Enterococcus faecalis

E. faecalis infections should be treated with ampicillin or amoxicillin as first-line therapy, while E. faecium infections require vancomycin or newer agents like linezolid or daptomycin due to intrinsic penicillin resistance. 1, 2, 3

Critical Species-Specific Differences

E. faecalis Treatment Approach

• Ampicillin 2 g IV every 4-6 hours is the gold standard for susceptible E. faecalis infections (MIC ≤8 mg/L), as most strains retain ampicillin susceptibility 2, 3

• For serious infections requiring bactericidal activity (endocarditis, bacteremia), combine ampicillin with gentamicin for synergy 1

  • Native valve endocarditis: ampicillin plus gentamicin for 4-6 weeks 1
  • Prosthetic valve endocarditis: minimum 6 weeks of combination therapy 1

• Alternative oral therapy: high-dose amoxicillin 1000 mg three times daily for less severe infections or chronic prostatitis 3

• Only 3% of E. faecalis strains are multidrug-resistant, and many vancomycin-resistant E. faecalis remain penicillin-susceptible 1

E. faecium Treatment Approach

• Intrinsic penicillin resistance is common in E. faecium, making ampicillin ineffective as first-line therapy 1

• Up to 95% of E. faecium strains express multidrug resistance to vancomycin, aminoglycosides, and penicillins 1

• First-line therapy for susceptible strains: vancomycin 30 mg/kg/day IV in 2 divided doses 3

• For vancomycin-resistant E. faecium (VRE):

  • Linezolid 600 mg IV/PO every 12 hours is the preferred agent with proven clinical efficacy 1, 3
  • Daptomycin 8-12 mg/kg/day IV is an alternative option 1, 3, 4
  • Quinupristin-dalfopristin has activity only against E. faecium (not E. faecalis) but is rarely used due to severe side effects including intractable muscle pain 1

Aminoglycoside Resistance Patterns

• For strains with high-level aminoglycoside resistance, the double β-lactam regimen (ampicillin 2 g IV every 4 hours plus ceftriaxone 2 g IV every 12 hours for 6 weeks) is reasonable for E. faecalis endocarditis 1

• This combination is effective for aminoglycoside-nonsusceptible E. faecalis strains 1

• Aminoglycoside resistance is increasingly common in both species, limiting traditional synergistic combinations 2

Predisposing Factors Differ by Species

• E. faecium BSI is independently associated with:

  • Previous penicillin use (aOR 1.99) or carbapenem use (aOR 2.35) 5
  • Hospital-acquired infection (aOR 2.58) 5
  • Biliary tract source (aOR 3.36) 5

• E. faecalis BSI is independently associated with:

  • Congestive heart failure (aOR 0.51) 5
  • Cerebrovascular disease (aOR 0.45) 5
  • Urinary tract source (aOR 0.49) 5

Critical Pitfalls to Avoid

• Never use cephalosporins alone for enterococcal coverage—they have no intrinsic activity despite in vitro synergy when combined with ampicillin 3

• Do not assume E. faecium has the same susceptibility profile as E. faecalis—E. faecium requires different empiric coverage due to intrinsic resistance 1, 6

• Differentiate colonization from true infection before initiating treatment, as antibiotic use itself promotes enterococcal colonization 2, 7

• Always obtain infectious disease consultation for enterococcal endocarditis management as standard of care 1

• For E. faecium endocarditis, the battle rages on with limited bactericidal options compared to E. faecalis, where treatment success is more achievable 6

Duration of Therapy

• Uncomplicated infections: 7-14 days 2
• Endocarditis or serious infections: 4-6 weeks minimum 1, 2
• Prosthetic valve involvement: minimum 6 weeks 1