A new IS element, IS1062, related to the enterococcal IS elements IS6770 and IS1252, was detected in the 3'-terminus of the surface exclusion gene, sep1, of sex pheromone plasmid pPD1 in Enterococcus faecalis. pPD1-bearing cells lack the surface exclusion function, probably as a consequence of this insertion. Analysis of pAD1 and pPD1 sequences (7.5 kb and 2.7 kb, respectively) downstream of their aggregation substance genes revealed no similarity in these DNA regions. Detailed DNA/DNA hybridization studies using DNA probes specific for various pAD1-encoded genes needed for plasmid transfer indicated that the sex pheromone plasmids have evolved by repeated recombination and insertion of diverse transposable elements which presumably account for recent acquisition of antibiotic resistances.

Sex-pheromone-plasmid-bearing strains of Enterococcus faecalis react with sex pheromone to induce the expression of an adhesin, the so-called aggregation substance, on their cell surface. Here we show that, by complementation studies, for sex-pheromone plasmid pADl, expression of the structural gene asal, coding for an aggregation substance, is mediated by a diffusible factor encoded on pAD1. We were able to demonstrate that a small open reading frame, traEl, is sufficient for transcription of the operon containing asal. A model for expression of asal under the influence of the positive regulator is presented, which is supported by our observation that regulation involves an all-or-nothing induction phenomenon, leading to cells either fully expressing asal or not at all.Plasmid-free strains of Enterococcus faecalis excrete short peptides (7 or 8 amino acids in length), the so-called sex pheromones, which can be 'sensed' by cells containing a corresponding sex-pheromone plasmid. These sex-pheromone-plasmid-bearing cells react by expressing a plasmidencoded adhesin, the so-called aggregation substance (AS), on their surface. By interaction of AS with a specific binding substance, which is also present on plasmid-free cells, large macroscopically visible aggregates form with the subsequent and highly efficient transfer of the plasmid. (Conjugative plasmids of E. faecalis not responding to sex pheromones are transferred in broth four orders or five orders of magnitude less efficiently than sex-pheromone plasmids.) After an E. faecalis cell has received a sex-pheromone plasmid, it shuts down the production of the corresponding sex pheromone, whereas sex pheromones specific to other plasmids continue to be produced. By this mechanism, a multitude of different sex-pheromone plasmids can accumulate in a single cell (see Clewell and Weaver 1989; Dunny, 1990). Little is known about the advantage those plasmids offer the cell; our recent data indicate that the adhesin might at least contribute to the virulence of E. fuecalis strains (Kreft et al., 1992).Obviously, the response to sex pheromones is strictly regulated. While, for the plasmid transfer itself few data are available, much more is known about the aggregation reaction. In the case of the most extensively studied sex-pheromone plasmid, pAD1, a region of about 12 kb has been sequenced, containing the genes for AS (asal; coding for a protein of 137 kDa; Galli et al., 1990)

No abstract

Aggregation substance (AS) of Enterococcus faecalis which is encoded by so-called sex pheromone plasmids enables the bacteria to bind to in vitro-cultured pig kidney tubular cells. It is reported that the presence of AS is not of pivotal importance for the ability of E. faecalis to cause infective endocarditis (EN). The lines of evidence for this are twofold: 1) sex pheromone plasmids and, therefore, the gene for AS were not present more often in epidemiologically unrelated strains of E. faecalis isolated from human cases of EN than in isolates from well-water (26 vs. 18%); 2) the presence of the adhesin did not correlate with the establishment of EN in an animal (rat) model. The data are discussed with respect to the specificity of interaction of AS with eukaryotic cells and the results of other studies.

A new IS element, IS1062, related to the enterococcal IS elements IS6770 and IS1252, was detected in the 3'-terminus of the surface exclusion gene, sep1, of sex pheromone plasmid pPD1 in Enterococcus faecalis. pPD1-bearing cells lack the surface exclusion function, probably as a consequence of this insertion. Analysis of pAD1 and pPD1 sequences (7.5 kb and 2.7 kb, respectively) downstream of their aggregation substance genes revealed no similarity in these DNA regions. Detailed DNA/DNA hybridization studies using DNA probes specific for various pAD1-encoded genes needed for plasmid transfer indicated that the sex pheromone plasmids have evolved by repeated recombination and insertion of diverse transposable elements which presumably account for recent acquisition of antibiotic resistances.