How do Enterococcus faecalis and Enterococcus faecium differ in epidemiology, typical infection sites, and antimicrobial susceptibility?

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Last updated: November 2, 2026 • View editorial policy

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Enterococcus faecalis vs faecium: Key Clinical Differences

E. faecium is significantly more resistant to antimicrobials and carries higher mortality than E. faecalis, requiring species-specific treatment approaches and heightened clinical vigilance.

Epidemiology & Clinical Distribution

Species Prevalence

  • E. faecalis remains the most common enterococcal isolate overall (46.7-94% of enterococcal infections) 1, 2
  • E. faecium is increasingly predominant in hospital-acquired infections, particularly in ICU settings and bloodstream infections (55.8% of BSIs) 3
  • E. faecium prevalence has risen dramatically in healthcare-associated infections, with VRE rates increasing from 8.1% (2012) to 19% (2018) in Europe 4

Patient Demographics & Risk Factors

E. faecalis infections are associated with:

  • Mitral valve endocarditis
  • Central venous line presence
  • Liver transplantation
  • Broader range of infection sources 4

E. faecium infections are associated with:

  • Hematologic malignancies
  • Neutropenia
  • Prior antibiotic exposure
  • Tricuspid valve endocarditis
  • Intra-abdominal infection sources (more concentrated origin pattern) 5, 3

Infection Sites

Common Sites by Species

E. faecalis:

  • Urinary tract infections (most common)
  • Intra-abdominal infections
  • Endocarditis (mitral valve)
  • Broader tissue distribution 1, 2

E. faecium:

  • Bloodstream infections (predominant)
  • Intra-abdominal infections
  • Device-associated infections
  • Endocarditis (tricuspid valve) 5, 3

Antimicrobial Susceptibility: Critical Differences

E. faecalis Susceptibility Profile

High susceptibility (>90-95%) to:

  • Ampicillin (100% in most studies) 6
  • Vancomycin (98.78% susceptible) 6
  • Daptomycin (>95%) 6
  • Linezolid (>95%) 6
  • Teicoplanin (>95%) 6
  • Tigecycline (>95%) 6
  • Nitrofurantoin (69.69% for UTI) 2
  • Fosfomycin (78.79% for UTI) 2

Resistance patterns:

  • Vancomycin resistance: 1.22-7.2% globally 4, 6
  • High-level aminoglycoside resistance: 54.55% 2
  • β-lactam resistance: 21.4% 1

E. faecium Susceptibility Profile

High susceptibility (>90%) ONLY to:

  • Linezolid (>90%) 6
  • Tigecycline (>90%) 6

Extensive resistance:

  • Ampicillin: 93.9% resistant (only 6.1% susceptible) 3
  • Vancomycin: 25.4% resistant globally, up to 53.25% in North America 6
  • β-lactams: 100% resistant 1
  • Fluoroquinolones: 100% resistant 1
  • Fosfomycin: 100% resistant 1
  • High-level streptomycin: 100% resistant 1
  • High-level aminoglycosides: 66.67% 2

Multidrug Resistance Patterns

E. faecium demonstrates significantly higher rates of:

  • MDR (multidrug-resistant) phenotypes
  • XDR (extensively drug-resistant) phenotypes
  • PDR (pandrug-resistant) phenotypes
  • Greater genomic plasticity with more antimicrobial resistance genes 5

E. faecalis shows comparatively lower MDR/XDR rates with larger core genome and more stable resistance patterns 5

Clinical Outcomes & Mortality

Mortality Risk

E. faecium infections carry significantly higher 30-day mortality than E. faecalis 3. Independent predictors of mortality include:

  • E. faecium species (independent risk factor)
  • Pitt Bacteremia Score
  • Charlson Comorbidity Index
  • XDR phenotype (longest hospital stays) 1, 3

E. faecium endocarditis specifically shows:

  • Higher mortality rates
  • Longer duration of bacteremia
  • Worse outcomes compared to E. faecalis endocarditis 4

Hospital Course

  • XDR isolates (predominantly E. faecium) associated with longest hospital stays
  • Non-MDR E. faecalis associated with shortest hospital stays
  • Overall improvement rate: 76.7% across both species 1

Treatment Implications by Species

For E. faecalis Infections

First-line options:

  • Ampicillin remains highly effective (100% susceptibility) 6
  • For UTI: Nitrofurantoin or fosfomycin are excellent choices 2
  • For serious infections: Ampicillin ± gentamicin (if susceptible)
  • Vancomycin if ampicillin-resistant 4

For E. faecium Infections

Limited effective options:

  • Linezolid 600 mg IV/PO q12h (strong recommendation for enterococcal infections) 4
  • High-dose daptomycin 8-12 mg/kg/day ± β-lactams for bacteremia 4
  • Tigecycline for intra-abdominal infections (NOT for bacteremia due to low serum levels) 4
  • Vancomycin only if susceptible (75% chance) 6

Critical Pitfalls to Avoid

  1. Never use tigecycline for E. faecium bacteremia - large volume of distribution results in inadequate serum levels despite tissue penetration 4
  2. Do not assume ampicillin efficacy for E. faecium - 93.9% are resistant 3
  3. Differentiate colonization from true infection before initiating anti-VRE therapy 4
  4. Species identification is mandatory - treatment differs dramatically between species 3
  5. For VRE UTI with ampicillin resistance: High urinary ampicillin concentrations (18-30g IV daily) may still achieve bactericidal activity with 88.1% clinical cure 4

Geographic Variation in Resistance

  • North America: Highest E. faecium vancomycin resistance (53.25%) 6
  • Asia: Highest linezolid resistance in E. faecium (2.9%) 6
  • ICU patients: Generally higher resistance rates across all antibiotics 6

Key Genomic Differences

E. faecium exhibits:

  • Smaller core genome
  • Greater plasmid replicon diversity
  • More antimicrobial resistance genes
  • Higher genomic plasticity and horizontal gene transfer capacity
  • More PVM-type virulence genes 5

E. faecalis retains:

  • Larger, more stable core genome
  • Classical virulence factors
  • Clonal relatedness in within-host isolates 5

References

Related Questions

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Professional Medical Disclaimer

This information is intended for healthcare professionals. Any medical decision-making should rely on clinical judgment and independently verified information. The content provided herein does not replace professional discretion and should be considered supplementary to established clinical guidelines. Healthcare providers should verify all information against primary literature and current practice standards before application in patient care. Dr.Oracle assumes no liability for clinical decisions based on this content.