COMPARATIVE-ANALYSIS OF 18 SEX-PHEROMONE PLASMIDS FROM ENTEROCOCCUS-FAECALIS - DETECTION OF A NEW INSERTION ELEMENT ON PPD1 AND IMPLICATIONS FOR THE EVOLUTION OF THIS PLASMID FAMILY

A new IS element, IS1062, related to the enterococcal IS elements IS67 70 and IS1252, was detected in the 3'-terminus of the surface exclusio n 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 substan ce genes revealed no similarity in these DNA regions. Detailed DNA/DNA hybridization studies using DNA probes specific for various pAD1-enco ded genes needed for plasmid transfer indicated that the sex pheromone plasmids have evolved by repeated recombination and insertion of dive rse transposable elements which presumably account for recent acquisit ion of antibiotic resistances.