Enterococcus faecalis cytolysin (Cyl)

Enterococcus faecalis cytolysin is a specialized two-peptide exotoxin produced by virulent strains of the Gram-positive bacterium Enterococcus faecalis. It belongs to the class of pore-forming toxins (PFTs) and is unique for its dual activity as both a bacteriocin (killing competing bacteria) and a hemolysin (lysing eukaryotic cells). The toxin is composed of two subunits, CylL_L and CylL_S, which undergo complex post-translational modifications before being secreted. Upon reaching a target cell, the subunits oligomerize to form stable pores in the plasma membrane, causing rapid cell death through osmotic lysis. In clinical medicine, the presence of cytolysin-producing E. faecalis in the gut has been strongly linked to the severity and high mortality rates of alcohol-associated hepatitis (AH). Research has demonstrated that neutralizing this toxin—either by using bacteriophages to eliminate the producing bacteria or by using specific antibodies to block the toxin's action—can significantly reduce liver injury and improve survival in preclinical models. Consequently, the Enterococcus faecalis cytolysin is a high-priority target for precision medicine approaches in treating severe liver diseases and multidrug-resistant enterococcal infections.

Other names

CylL/CylSCylLL/CylLSEnterococcal cytolysinHemolysin/bacteriocinTwo-component cytolysin

The Enterococcus faecalis cytolysin is a two-component toxin consisting of two post-translationally modified peptides, CylL_L and CylL_S. These subunits assemble on the target cell membrane (such as hepatocytes or erythrocytes) to form a transmembrane pore. This pore disrupts the osmotic balance of the cell, leading to an influx of ions and water, which results in cell swelling and eventual osmotic lysis. In the context of liver disease, this toxin directly induces hepatocyte death, exacerbating inflammation and liver injury.