What type of bacteria is Enterococcus faecalis?

Enterococcus faecalis: Bacterial Classification and Characteristics

Enterococcus faecalis is a Gram-positive, catalase-negative, facultative anaerobic coccus that is part of the normal intestinal flora but can act as an opportunistic pathogen in various clinical settings. 1

Taxonomic Classification

• Kingdom: Bacteria
• Phylum: Firmicutes
• Class: Bacilli
• Order: Lactobacillales
• Family: Enterococcaceae
• Genus: Enterococcus
• Species: E. faecalis

Microbiological Characteristics

• Gram-positive cocci (spherical bacteria)
• Typically arranged in pairs or short chains
• Non-spore forming
• Facultative anaerobe (can grow with or without oxygen)
• Catalase-negative
• Able to survive extreme environmental conditions:
  • Temperature range: 5-65°C
  • pH range: 4.5-10.0
  • High salt concentrations 1

Habitat and Distribution

• Primary habitat: Gastrointestinal tract of humans and animals
• Also found in:
  • Oral cavity
  • Vagina (less frequently)
  • Environmental sources 2

Clinical Significance

E. faecalis is one of the most prevalent bacteria among aerobic Gram-positive bacteria isolated in intra-abdominal infections, representing approximately 15.9% of all aerobic isolates 3. It is found in:

• Community-acquired infections (13.9% of cases)
• Hospital-acquired infections (22.3% of cases) - more prevalent in this setting 3
• Intra-abdominal infections - found in 12% of patients with complicated intra-abdominal infections 3
• Endocarditis - one of the common causes of enterococcal endocarditis 3
• Urinary tract infections
• Hepatobiliary sepsis
• Surgical wound infections
• Bacteremia
• Endodontic infections - present in 30-89% of teeth with post-endodontic treatment failures 4

Antimicrobial Resistance

E. faecalis can develop resistance to multiple antibiotics:

• Intrinsic resistance to cephalosporins 5
• Some strains produce β-lactamase (inhibited by β-lactamase inhibitors like sulbactam and clavulanic acid) 3
• Can acquire resistance to:
  • Ampicillin
  • Gentamicin
  • Vancomycin (though less commonly than E. faecium) 3

Virulence Factors

• Extracellular protein Esp - aids in colonization of the host
• Aggregation substances (Agg) - facilitate adherence to host tissues
• Cytolysin - a pore-forming exotoxin that can lyse both bacterial and eukaryotic cells 1, 6
• Ability to penetrate dentinal tubules and survive as a monoculture 4

Treatment Considerations

For infections caused by E. faecalis:

• First-line treatment: Ampicillin (for susceptible strains) 5
• Alternative options:
  • Vancomycin (for ampicillin-resistant, vancomycin-susceptible strains) 5
  • Linezolid or tigecycline (for vancomycin-resistant strains) 3
  • Daptomycin (especially at higher doses of 8-12 mg/kg/day) 3, 5, 7

Emerging Therapeutic Approaches

Research is exploring novel approaches to combat antibiotic-resistant E. faecalis:

• Bacteriophage therapy - using specific viruses that target and kill E. faecalis 4, 8
• Combination therapies - synergistic effects observed between vancomycin and aminoglycosides against many strains of enterococci 9

E. faecalis represents a perfect example of a commensal organism that can transition to an opportunistic pathogen, particularly in healthcare settings and in immunocompromised hosts, highlighting the importance of proper infection control measures and appropriate antimicrobial stewardship.