Why does Staphylococcus aureus secrete an Enterococcus faecalis-specific pheromone?
The long known fact that Staphylococcus aureus can secrete a peptide (staph-cAM373) which acts as a sex pheromone for strains of E. faecalis carrying the sex pheromone plasmid pAM373 was studied in detail. 85 of 100 independent isolates of S. aureus produced an activity inducing the pAM373 encoded adhesin resulting in a clumping reaction of E. faecalis (i.e. secreted staph-cAM373), but not a single one of 100 independent isolates of coagulase-negative Staphylococci possessed this activity. The production of peptides acting as sex pheromone for E. faecalis was observed only for sex pheromone plasmid pAM373, but not for sex pheromone plasmids pAD1 and pPD1. It was shown that the amount of staph-pAM373 produced during growth paralleled cell mass, therefore this peptide should not be used as a cell density indicator by S. aureus (i.e. has no quorum sensing function). The potential function of staph-cAM373 to trigger gene transfer from Escherichia faecalis to S. aureus is discussed.