Cefixime Susceptibility Against E. coli and E. faecalis
Cefixime is effective against E. coli but NOT against Enterococcus faecalis (E. faecilis). You should never use cefixime to treat enterococcal infections.
E. coli Susceptibility
Cefixime demonstrates excellent activity against E. coli, including many resistant strains:
- FDA-approved indication: Cefixime is active against E. coli in both in vitro and clinical infections 1
- Clinical efficacy: Greater than 99% of E. coli isolates are susceptible to cefixime, including ampicillin-resistant strains 2
- Spectrum: Effective against most Enterobacteriaceae (87.7% susceptible at ≤1.0 μg/mL) 3
Important caveat: Cefixime may have limited activity against E. coli producing extended-spectrum β-lactamases (ESBLs) 1. Always check local resistance patterns before empiric use, as E. coli resistance to cephalosporins is increasing 4.
E. faecalis Resistance
Enterococcus faecalis is intrinsically resistant to cefixime - this is a critical clinical point:
- FDA label explicitly states: "Enterococcus species are resistant to cefixime" 1
- Multiple studies confirm: Staphylococcus, Pseudomonas aeruginosa, and Enterococcus faecalis were all resistant to cefixime 5
- Mechanism: Enterococci are resistant to all cephalosporins, including third-generation agents like cefixime 3, 6
Why This Matters Clinically
When treating intra-abdominal or urinary infections where enterococci may be present:
- Community-acquired infections: Empiric anti-enterococcal coverage is NOT necessary 4
- Healthcare-associated infections: You MUST add anti-enterococcal therapy (ampicillin, piperacillin-tazobactam, or vancomycin) 4
- High-risk patients: Those with postoperative infections, prior cephalosporin exposure, immunosuppression, or valvular heart disease require enterococcal coverage 4
Bottom line: If you're considering cefixime and E. faecalis is a concern, you need a different antibiotic. For enterococcal coverage, use ampicillin (first-line), piperacillin-tazobactam, or vancomycin based on susceptibility testing 4.