Impact of the agr quorum-sensing system on adherence to polystyrene in Staphylococcus aureus

Biofilm formation by Staphylococcus aureus is a serious problem in nosocomial infections. There are great differences in the capacity of S. aureus to express biofilms, but the reasons are unknown. In all, 105 S. aureus strains were tested for a correlation between the agr quorum-sensing system phenotype and the ability of S. aureus to adhere to polystyrene. Some 78% of agr-negative, but only 6% of agr-positive, strains formed a biofilm, demonstrating a profound impact of agr on biofilm formation. This result was confirmed with defined agr mutants and by inhibition of agr with quorum-sensing blockers. The observed effect was not due to differential expression of the autolysin Atl or of the exopolysaccharide polysaccharide intercellular adhesin but seemed to be caused, at least in part, by the surfactant properties of delta-toxin. The detected biofilm-enhancing effect of S. aureus quorum-sensing blockers call into question the proposed therapeutic use of such substances.

Inducible expression and cellular location of AgrB, a protein involved in the maturation of the staphylococcal quorum-sensing pheromone

AgrB has been suggested to be responsible for the posttranslational modification in staphylococci that leads to the production of the thiolactone-containing agr peptide pheromone. We demonstrate that AgrB is located in the cytoplasmic membrane. Vectors were constructed for the xylose-inducible overexpression of agrB, and of agrB and agrD together. A Staphylococcus epidermidis strain deleted for agr and containing these vectors was assayed for AgrB protein and pheromone production. The lack of adequate pheromone production suggests the involvement of additional factors in the production of the agr pheromone.