Enterococcal cytolysin: activities and association with other virulence traits in a pathogenicity island.

Enterococcal cytolysin is a structurally novel bacterial toxin expressed by some strains of E. faecalis and is distantly related to the class of bacteriocins known as lantibiotics. The cytolysin can be encoded by large pheromone-responsive plasmids, or on the chromosome within pathogenicity island. It is produced by a complex process that involves the products of eight genes, designated cylR1, cylR2, cylLL, cylLS, cylM, cylB, cylA, and cylI. The cytolysin toxin, maturation and regulatory genes are organized into two divergent transcripts: a structural transcript cylLLLSMBAI, and a regulatory transcript cylR1R2. The active cytolysin subunits, CylLL" and CylLS", are synthesized ribosomally as non-identical peptides, post-translationally modified, then secreted and activated. The cytolysin operon is repressed by the activities of two proteins, CylR1 and CylR2, and derepressed by a quorum-sensing process involving secreted autoinducer CylLS". The cytolysin operon within the E. faecalis pathogenicity island is associated with other virulence determinants, including aggregation substance and enterococcal surface protein, Esp.