Antagonistic Donor Density Effect Conserved in Multiple Enterococcal Conjugative Plasmids.

Area of Science:

• Microbiology
• Bacterial genetics
• Molecular biology

Background:

• Enterococcus faecalis is a major cause of hospital-acquired infections.
• This bacterium readily acquires and transfers antibiotic resistance and virulence genes via conjugative plasmids.
• Plasmid transfer is regulated by signaling peptides, including recipient-produced pheromones and donor-produced inhibitors.

Purpose of the Study:

• To investigate if plasmids pAD1 and pAM373 in Enterococcus faecalis exhibit quorum-sensing behaviors similar to pCF10.
• To determine the role of donor density and inhibitor peptides in regulating conjugation of pAD1 and pAM373.
• To propose models for the regulation of conjugation operons in pAD1 and pAM373.

Main Methods:

• Comparative analysis of regulatory features of plasmids pAD1, pAM373, and pCF10.
• Experimental induction of conjugation in Enterococcus faecalis strains carrying pAD1 and pAM373 at varying donor cell densities.
• Assessing conjugation frequencies and operon induction in the presence and absence of exogenous inhibitor peptides.

Main Results:

• High donor cell densities significantly decreased conjugation operon induction and conjugation frequencies for both pAD1 and pAM373.
• The addition of exogenous inhibitor peptides restored conjugation frequencies in high-donor-density cultures.
• These findings confirm that inhibitor peptides act as density-dependent signals for donor cells.

Conclusions:

• Plasmids pAD1 and pAM373, like pCF10, utilize quorum-sensing mechanisms involving inhibitor peptides to regulate conjugation.
• Donor cell density, mediated by inhibitor peptide concentration, controls plasmid transfer efficiency.
• Targeting these bacterial signaling pathways presents a potential alternative strategy to combat antibiotic resistance.