Is carbapenem (a type of antibiotic) effective against Enterococcus?

Carbapenems Are Not Effective Against Enterococcus

Carbapenems lack reliable activity against Enterococcus species and should not be used as monotherapy when enterococcal coverage is needed. According to the FDA drug label for meropenem, while it has activity against many gram-positive and gram-negative bacteria, Enterococcus faecalis is only listed as susceptible for "vancomycin-susceptible isolates only" and other Enterococcus species are not included in its spectrum of activity 1.

Carbapenem Activity Against Enterococcus

Carbapenems have the following characteristics regarding enterococcal coverage:

• Group 1 carbapenems (ertapenem) have no activity against Enterococcus species 2
• Group 2 carbapenems (imipenem/cilastatin, meropenem, doripenem) have limited activity:
  • They have only "inhibitory activity" against enterococci, not reliable bactericidal action 3
  • Meropenem's FDA label specifically lists only vancomycin-susceptible E. faecalis as susceptible, not other enterococcal species 1
  • Carbapenems "lack activity against Enterococcus faecium" 4

Clinical Implications

This lack of reliable enterococcal coverage has important clinical implications:

1. For intra-abdominal infections: When enterococcal coverage is needed, especially in hospital-acquired infections:

   • Ampicillin may need to be added to regimens (e.g., ceftriaxone-metronidazole) that would otherwise not cover enterococcus 2
   • For vancomycin-resistant Enterococcus (VRE), linezolid (for monomicrobial infection) or tigecycline (for polymicrobial infection) is recommended 2

2. For empiric therapy: When enterococcal coverage is needed:

   • Piperacillin-tazobactam is often preferred over carbapenems for severe infections due to its broader spectrum that includes enterococci 2
   • For hospital-acquired infections in critically ill patients, guidelines recommend piperacillin, tigecycline, or a carbapenem plus teicoplanin 2

Enterococcal Resistance Patterns

Enterococcal resistance is a significant concern:

• Enterococci are more prevalent in hospital-acquired infections (22.3%) than community-acquired infections (13.9%) 2
• Antimicrobial resistance among enterococcal isolates (ampicillin, gentamicin, or vancomycin resistance) is mostly found in nosocomial (postoperative or tertiary) peritonitis 2
• Poor outcomes have been documented among patients with enterococcal infections, particularly in postoperative intra-abdominal infections 2

Recommendations for Infections Potentially Involving Enterococcus

When treating infections where Enterococcus is a concern:

1. For community-acquired infections: Empiric enterococcal coverage is generally not recommended 2

2. For hospital-acquired or postoperative infections:

   • Consider agents with reliable enterococcal activity (piperacillin-tazobactam, ampicillin-sulbactam)
   • If using a carbapenem or cephalosporin regimen, consider adding specific anti-enterococcal agents when needed
   • For VRE infections, use linezolid or tigecycline based on whether the infection is monomicrobial or polymicrobial 2

In summary, carbapenems should not be relied upon for enterococcal coverage, and alternative or additional agents should be used when enterococcal infection is suspected or confirmed.