GENETIC-STRUCTURE OF THE ENTEROCOCCUS-FAECALIS PLASMID PAD1-ENCODED CYTOLYTIC TOXIN SYSTEM AND ITS RELATIONSHIP TO LANTIBIOTIC DETERMINANTS

Pheromone-responsive conjugative plasmids are unique to the species En terococcus faecalis. Many pheromone-responsive plasmids, including tho se frequently isolated from sites of infection, express a novel cytoly sin that possesses both hemolytic and bacteriocin activities. Further, this cytolysin has been shown to be a toxin in several disease models . In the present study, nucleotide sequence determination, mutagenesis , and complementation analysis were used to determine the organization of the E. faecalis plasmid pAD1 cytolysin determinant. Four open read ing frames are required for expression of the cytolysin precursor (cyl L(L), cylL(S), cylM, and cylB). The inferred products of two of these open reading frames, CylL(L) and CylL(S), constitute the cytolysin pre cursor and bear structural resemblance to posttranslationally modified bacteriocins termed lantibiotics. Similarities between the organizati on of the E. faecalis cytolysin determinant and expression units for l antibiotics exist, indicating that the E. faecalis cytolysin represent s a new branch of this class and is the first known to possess toxin a ctivity.