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

Biofilm formation by Staphylococcus aureus is a serious problem in nosocomi al infections. There are great differences in the capacity of S. aureus to express biofilms, but the reasons are unknown. In all, 105 S. aureus strain s were tested for a correlation between the agr quorum-sensing system pheno type 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, demonstra ting a profound impact of agr on biofilm formation. This result was confirm ed with defined agr mutants and by inhibition of agr with quorum-sensing bl ockers. The observed effect was not due to differential expression of the a utolysin Atl or of the exopolysaccharide polysaccharide intercellular adhes in 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 su bstances.