Cephalexin Does NOT Cover Enterococcus faecalis
No, cephalexin does not provide effective coverage for E. faecalis UTI and the antibiotic should be changed based on culture results. The FDA drug label explicitly states that "most strains of enterococci (Enterococcus faecalis) are resistant to cephalosporins, including cephalexin" 1. This is a critical treatment failure scenario requiring immediate antibiotic adjustment.
Why Cephalexin Fails Against E. faecalis
- Intrinsic resistance mechanism: E. faecalis possesses inherent resistance to all cephalosporins due to low-affinity penicillin-binding proteins that prevent cephalosporins from inhibiting bacterial cell wall synthesis 1
- This is not acquired resistance—it is a fundamental characteristic of enterococcal species that makes cephalosporins ineffective regardless of in vitro susceptibility testing 1
Recommended Antibiotic Switch for E. faecalis UTI
First-Line Options (Access Group Antibiotics):
For uncomplicated lower UTI:
- Nitrofurantoin 100 mg orally every 6 hours for 5-7 days is highly effective for E. faecalis cystitis with MIC ≤16 mg/L, achieving excellent urinary concentrations 2
- Amoxicillin 500 mg PO every 8 hours or ampicillin (if susceptible with penicillin MIC ≤8 mg/L) are drugs of choice for enterococcal infections 2
- Fosfomycin 3g PO single dose is FDA-approved specifically for E. faecalis UTI 2
For complicated UTI or pyelonephritis:
- Ampicillin 2g IV every 4-6 hours is the standard treatment when the organism is susceptible 2
- Amoxicillin-clavulanate is listed as an appropriate choice for lower UTI in current guidelines 3
Alternative Options if Penicillin-Allergic:
- Vancomycin 30 mg/kg per 24h IV in 2 divided doses shows low resistance rates against E. faecalis 2
- Linezolid has excellent activity against E. faecalis including vancomycin-resistant strains 2
Critical Clinical Considerations
- Duration matters: Treat for 7-14 days depending on whether this is simple cystitis versus complicated UTI (14 days for men when prostatitis cannot be excluded) 3
- Avoid nitrofurantoin for pyelonephritis: It achieves inadequate tissue penetration and should only be used for lower UTI/cystitis 2
- Differentiate E. faecalis from E. faecium: E. faecalis is generally more susceptible to ampicillin (only 3% multidrug-resistant) compared to E. faecium (up to 95% multidrug-resistant) 2
- Fluoroquinolones have high resistance: 46-47% of E. faecalis strains show ciprofloxacin resistance, particularly in hospital-acquired infections and patients from urology departments 4
Common Pitfall to Avoid
Do not continue cephalexin simply because the patient is clinically improving—this represents either spontaneous resolution or inadequate treatment that risks progression to complicated infection, particularly in men where prostatic involvement is common 3. The culture result definitively indicates treatment failure risk and mandates antibiotic change 1.