What antibiotics (abx) are recommended for treating blood cultures positive for Enterococcus Faecalis and Staphylococcus epidermidis?

Treatment of Polymicrobial Bacteremia with Enterococcus Faecalis and Staphylococcus Epidermidis

For blood cultures positive with both Enterococcus faecalis and Staphylococcus epidermidis, initiate ampicillin (if susceptible) or vancomycin (if ampicillin-resistant or methicillin-resistant S. epidermidis) as monotherapy, as both organisms will be covered by a single agent targeting the enterococcus.

Initial Antibiotic Selection

For Ampicillin-Susceptible E. Faecalis

• Ampicillin 2 g IV every 4 hours is the drug of choice for ampicillin-susceptible enterococci and will also provide coverage for methicillin-susceptible S. epidermidis 1.
• Ampicillin is preferred over other penicillins because MICs are typically two to four times lower than penicillin G for enterococcal infections 2.
• This single-agent approach covers both organisms without requiring combination therapy for uncomplicated bacteremia 1.

For Ampicillin-Resistant or Methicillin-Resistant Organisms

• Vancomycin is the drug of choice if E. faecalis is ampicillin-resistant or if S. epidermidis is methicillin-resistant 1, 3.
• Virtually all S. epidermidis isolates are susceptible to vancomycin, and it provides reliable coverage for both organisms 3.
• Vancomycin should be dosed at 30 mg/kg/day IV in 2 divided doses for optimal efficacy 1, 2.

Role of Combination Therapy

• Combination therapy with an aminoglycoside (gentamicin) is NOT necessary for uncomplicated bacteremia without endocarditis 1.
• The role of combination therapy (cell wall-active antimicrobial plus aminoglycoside) for enterococcal catheter-related bloodstream infection without endocarditis remains unresolved 1.
• If catheter salvage is attempted, combination therapy with gentamicin plus ampicillin may be more effective than monotherapy 1.

Treatment Duration and Monitoring

• A 7-14 day course of therapy is recommended for uncomplicated bacteremia when the catheter is removed 1.
• Remove any short-term intravascular catheters immediately 1.
• For long-term catheters, removal is indicated if there is insertion site infection, suppurative thrombophlebitis, sepsis, endocarditis, persistent bacteremia (>72 hours), or metastatic infection 1.

Critical Assessment for Endocarditis

• Obtain transesophageal echocardiography (TEE) if any of the following are present 1:
  • New cardiac murmur or embolic phenomena
  • Prolonged bacteremia or fever >72 hours despite appropriate antibiotics
  • Radiographic evidence of septic pulmonary emboli
  • Presence of prosthetic valve or other endovascular foreign bodies
• The risk of endocarditis with enterococcal bacteremia is relatively low (1.5% in one large study), but persistent bacteremia >4 days is independently associated with mortality 1.
• E. faecalis carries higher endocarditis risk than E. faecium 1.

Alternative Regimens for Resistant Organisms

• For ampicillin- and vancomycin-resistant enterococci, use linezolid or daptomycin based on susceptibility results 1.
• Linezolid 600 mg IV/PO every 12 hours is effective against vancomycin-resistant enterococci 4.
• Daptomycin 6 mg/kg/day IV is an alternative, though it may have less prostatic penetration if that is a concern 2, 5.

Common Pitfalls to Avoid

• Do not add gentamicin routinely unless attempting catheter salvage or treating confirmed endocarditis, as it adds nephrotoxicity risk without proven benefit in uncomplicated bacteremia 1.
• Do not assume methicillin susceptibility in S. epidermidis without reliable susceptibility testing, as nosocomial isolates are frequently methicillin-resistant and may appear susceptible unless proper methods are used 3.
• Do not use cephalosporins as monotherapy for this polymicrobial infection, as they lack reliable enterococcal coverage 1.
• Monitor for persistent bacteremia with follow-up blood cultures at 72 hours; persistence mandates catheter removal and extended evaluation for endocarditis 1.