Enterococcus faecalis

Metal Dependencies#

E. faecalis has a sophisticated relationship with metals.

Manganese: Unlike most bacteria that rely primarily on iron, E. faecalis uses manganese as a key cofactor for superoxide dismutase (MnSOD) and as a substitute for iron in many metabolic enzymes. This manganese-centered metabolism makes it inherently resistant to iron limitation by the host (nutritional immunity).

Iron: Required for some redox enzymes but not as critical as for most Gram-negatives, contributing to E. faecalis resilience in iron-restricted environments.

Zinc susceptibility: E. faecalis is susceptible to zinc-enhanced antimicrobial strategies. A zinc-potentiated halogenated phenazine disrupted metal homeostasis in E. faecalis by causing intracellular zinc and iron accumulation, manganese depletion, and ultimately bacterial killing. This mis-metallation mechanism represents a novel antimicrobial approach (,^{[1]Kajfasz 2026 — Zinc-Enhanced Activity of an Antimicrobial Halogenated Phenazine Against Streptococcus mutans and Other Gram-Positive BacteriaJessica K Kajfasz, Hannah B Hosay, Qiwen Gao et al. · 2026Open reference 1 ↓} in-vitro).

Key Enzymes and Virulence Factors#

Tyrosine decarboxylase (TyrDC): The enzyme that converts L-DOPA (levodopa) to dopamine in the gut. This is the first step of an interspecies relay where E. faecalis produces dopamine, which is then dehydroxylated to m-tyramine by Eggerthella lenta. The combined pathway significantly reduces levodopa bioavailability in Parkinson's patients.

AFMT (alpha-fluoromethyltyrosine) can selectively inhibit bacterial TyrDC without affecting host DOPA decarboxylase (,^{[2]Maini Rekdal 2019 -- Discovery and Inhibition of an Interspecies Gut Bacterial Pathway for Levodopa MetabolismVayu Maini Rekdal, Emily N Bess, Jordan E Bisanz et al. · 2019Open reference 2 ↓} in-vitro).

Extracellular superoxide: E. faecalis produces extracellular superoxide and hydrogen peroxide that generate reactive oxygen species (ROS), causing oxidative DNA damage in nearby colonocytes. This mechanism contributes to genomic instability and colorectal carcinogenesis (,^{[3]Immune System, Microbiota, and Microbial Metabolites: The Unresolved Triad in Colorectal Cancer MicroenvironmentHanus M, Parada-Venegas D, Landskron G et al. · 2021Open reference 3 ↓} expert-opinion).

Cytolysin: A two-peptide bacteriocin/toxin that lyses eukaryotic cells and is associated with increased disease severity in enterococcal infections. Gelatinase (GelE): A metalloprotease that degrades host tissue proteins, facilitating invasion and biofilm maturation.

Biofilm formation: E. faecalis forms robust biofilms on medical devices and mucosal surfaces, contributing to antibiotic tolerance and chronic infection.

Ecological Role#

In the healthy gut, E. faecalis is a minor member of the Firmicutes community, kept in check by competitive exclusion from dominant anaerobes and antimicrobial peptides. It becomes ecologically significant when.

Antibiotic disruption: Broad-spectrum antibiotics (especially vancomycin, paradoxically) can eliminate competing commensals and allow E. faecalis expansion. In EAE (MS model), E. faecalis did not ameliorate neuroinflammation when administered, confirming it lacks the anti-inflammatory properties of beneficial commensals (,^{[4]Mining the microbiota to identify gut commensals modulating neuroinflammation in a mouse model of multiple sclerosisPaola Bianchimano, Graham J. Britton, David S. Wallach et al. · 2022Open reference 4 ↓} animal-model).

Metal-Driven Inflammation: Enriched in IBD, particularly UC, where disrupted barrier function and Oxidative Stress create favorable conditions.

Reproductive tract Dysbiosis: Significantly enriched in the vaginal and intestinal microbiota of women with adenomyosis and infertility (,^{[5]Ponomaryova 2022 — Changes in microbiota of genital tract and intestines in patients with adenomyosis and infertilityPonomaryova IG, Lisyana TO, Trokhimovych OV et al. · 2022Open reference 5 ↓} cross-sectional).

Enriched in:#

Colorectal cancer: Cataloged as a pro-tumor bacterium through extracellular superoxide/ROS-mediated DNA damage, contributing to genomic instability (,^{[3]Immune System, Microbiota, and Microbial Metabolites: The Unresolved Triad in Colorectal Cancer MicroenvironmentHanus M, Parada-Venegas D, Landskron G et al. · 2021Open reference 3 ↓} expert-opinion;,^{[6]Antitumor Effects of Fecal Microbiota Transplantation: Implications for Microbiome Modulation in Cancer TreatmentHui Xu, Chenxi Cao, Yuqing Ren et al. · 2022Open reference 6 ↓} expert-opinion).

Adenomyosis/infertility: Enriched in vaginal and intestinal microbiota of women with adenomyosis alongside E. coli, S. epidermidis, and Candida (,^{[5]Ponomaryova 2022 — Changes in microbiota of genital tract and intestines in patients with adenomyosis and infertilityPonomaryova IG, Lisyana TO, Trokhimovych OV et al. · 2022Open reference 5 ↓} cross-sectional).

Ulcerative colitis: Markedly elevated in UC patients, distinguishing UC from CD taxonomically (,^{[7]Diagnosis of Crohn's Disease and Ulcerative Colitis Using the MicrobiomeKang DY, Park JL, Yeo MK et al. · 2023Open reference 7 ↓} cross-sectional). Pancreatic cancer: Found in duodenal microbiota of PC patients (,^{[8]Microbiome as a biomarker and therapeutic target in pancreatic cancerGhazaleh Pourali, Danial Kazemi, Amir Shayan Chadeganipour et al. · 2024Open reference 8 ↓} expert-opinion).