Origin of Enterococcus faecalis
Enterococcus faecalis originates from the normal gastrointestinal flora of humans and animals, where it exists as a commensal organism at concentrations of 10⁵-10⁷ colony-forming units per gram of stool. 1
Primary Reservoir and Natural Habitat
- E. faecalis is a normal inhabitant of the human intestinal tract, colonizing from the first days of life and persisting throughout the lifespan 1, 2
- The bacterium exists in a remarkable array of environments including soil, food, water, and as part of the normal gut flora of both humans and animals 1
- Less frequently, enterococci can be found colonizing the vagina and oral cavity 3
Pathogenic Acquisition: The Two-Stage Process
The current understanding reveals that enterococcal infections follow a two-stage pathogenic process rather than simple endogenous spread 1:
Stage 1: Initial Colonization
- Gastrointestinal tract colonization occurs with enterococcal strains that possess virulence traits and/or antibiotic resistance 1
- This colonization can be endogenous (patient's own flora) or exogenous (hospital-acquired strains transmitted from other patients or the environment) 1
Stage 2: Population Expansion and Invasion
- The colonizing population spreads within the GI tract, often facilitated by antibiotic elimination of competing bacteria 1
- Subsequently, tissue invasion occurs from the gastrointestinal tract reservoir in susceptible patients 1
Healthcare-Associated vs. Community-Acquired Origins
Hospital Environment
- In healthcare settings, E. faecalis is predominantly nosocomial, found in 22.3% of hospital-acquired intra-abdominal infections versus 13.9% in community-acquired infections 4
- Risk factors for acquiring pathogenic hospital strains include: previous antibiotic therapy, prolonged hospitalization, ICU admission, severe underlying illness, invasive procedures, gastrointestinal surgery, organ transplantation, and proximity to VRE-positive patients 4
Community Setting
- While present in community-acquired infections, E. faecalis is less prevalent and typically represents endogenous flora becoming pathogenic under specific conditions 4
- Patients with underlying urological conditions, immunocompromise, or chronic medical conditions are at higher risk 4
Clinical Significance of Origin
- For immunocompetent individuals, enterococcal strains without virulence traits or antibiotic resistance transferred via food or probiotics represent minimal risk 1
- In severely immunocompromised patients, even commensal strains cannot be completely excluded as potential pathogens 1
- The bacterium's ability to translocate from the GI tract to various tissues and organs depends on host susceptibility factors and the presence of medical devices 5, 3
Common Pitfall to Avoid
Do not assume all E. faecalis infections are endogenously acquired from the patient's own flora—hospital transmission of virulent, antibiotic-resistant strains is increasingly common and represents a distinct epidemiological pattern requiring infection control measures 1.