Is Enterococcus faecium (E. faecium) a known colonizer of the human gut?

Enterococcus faecium as a Known Gut Colonizer

Yes, Enterococcus faecium is a known colonizer of the human gut, serving as a commensal organism in the gastrointestinal tract of humans and animals. 1

Colonization Characteristics

• E. faecium is one of the most abundant enterococcal species found in the human fecal microbiota, alongside Enterococcus faecalis 1
• Longitudinal surveys have consistently shown that Enterococcus species, including E. faecium, are abundant colonizers in very early stages of microbiome establishment in both preterm and term infants 2
• E. faecium colonizes humans and a wide range of animals, demonstrating its adaptability to various host environments 3
• The species has evolved to endure numerous environmental stresses, allowing it to persist as a gut commensal 3

Clinical Significance of E. faecium Colonization

• While E. faecium exists as a commensal in the gut, it can also emerge as an opportunistic pathogen, particularly in healthcare settings 4
• The emergence of vancomycin-resistant E. faecium (VRE) has become a significant clinical concern, as these strains cause many hospital-acquired infections 3
• Clonal complex 17 (CC17) E. faecium strains have adapted specifically to hospital environments and are responsible for a significant proportion of hospital-associated infections 4
• E. faecium is more prevalent in healthcare-associated infections (22.3%) compared to community-acquired infections (13.9%) 5

Factors Affecting Colonization

• Antibiotic treatment depletes broad communities of commensal microbes from the GI tract, allowing resistant enterococci to densely colonize the gut 1
• Prolonged hospitalization, ICU admission, severe underlying illness, invasive procedures, gastrointestinal surgery, organ transplantation, and proximity to other VRE-positive patients are risk factors for VRE acquisition 6
• Prolonged antibiotic therapy (>10 days) increases the risk of enterococcal colonization and potential superinfection with resistant strains 5

Genomic Dynamics During Colonization

• E. faecium demonstrates considerable genomic flexibility during gut colonization, with frequent horizontal gene transfer and recombination events 7
• The evolutionary rate of E. faecium during colonization has been estimated at 12.6 to 25.2 single-nucleotide polymorphisms (SNPs) per genome per year 7
• Patients can be concurrently colonized by multiple distinct lineages of E. faecium 7
• The accessory genome of E. faecium shows considerable variation due to gene gain and loss events during colonization 7

Recent Taxonomic Considerations

• Recent research suggests that E. faecium strains colonizing the human gut (previously classified as clade B) may actually correspond to a different species, Enterococcus lactis 8
• E. lactis strains from clinical origins are generally pan-susceptible to antibiotics and lack the infection-associated virulence markers typical of hospital-adapted E. faecium 8

Infection Control Implications

• When VRE is isolated from a clinical specimen, confirmation of vancomycin resistance and prompt implementation of appropriate isolation precautions are essential 6
• Active surveillance in high-risk units and culture surveys of stools or rectal swabs may be necessary for controlling VRE transmission 6
• Judicious use of antibiotics is critical to prevent selection pressure for resistant enterococcal strains 6