Conjugative Plasmid Transfer From Enterococcus faecalis to Oral Streptococcal Species

Objectives: Objectives. Enterococcus faecalis and oral streptococci cohabit oral biofilms. Streptococcus gordonii strain produces the pheromone-like peptide s.g.cAM373 (SVFILAA) that induces a mating response in E. faecalis cells carrying cognate responsive plasmid pAM373 derivatives. This response, which includes the plasmid-encoded synthesis of surface aggregation substance and plasmid transfer functions, facilitates conjugative transfer of pAM373 derivatives and co-resident plasmid DNA to S. gordonii recipient cells. We hypothesize that under conditions of close bacterial proximity that occur in multispecies oral biofilms, s.g.cAM373 may also induce E. faecalis cells carrying pheromone-responsive plasmids to conjugatively transfer DNA to neighboring non-pheromone-producing streptococcal recipients.
Methods: Methods. E. faecalis/pAM378/pAMS470 cells were incubated with synthetic s.g.cAM373 (SVFILAA), reverse peptide (AALIFVS), or peptide-free medium and then examined for their abilities to conjugatively transfer plasmid DNA to non-pheromone producing recipients via 2-hour filter matings in the presence of DNAse, to control for transformation. After selection of putative transconjugants on antibiotic agar, plasmid preparations were used to confirm the presence of transferred DNA in representative colonies.
Results: Results. Filter matings showed that synthetic SVFILAA induced E. faecalis/pAM378/pAMS470 cells to conjugatively transfer plasmid DNA to non-pheromone producing Streptococcus mutans, Streptococcus sanguinis, Streptococcus anginosus, and Streptococcus suis recipient cells at frequencies at least two to three orders of magnitude higher than frequencies seen with AALIFVS or peptide-free controls.
Conclusions: Conclusion. These in vitro results suggest that peptide-mediated signals and responses between S. gordonii and E. faecalis may facilitate conjugative transfer of plasmid DNA to unrelated neighboring species in oral biofilms. Such peptide-induced conjugative DNA transfer may contribute to the horizontal dissemination of antibiotic resistance and/or virulence determinants among the oral microbiota.