Role of agr (RNAIII) in Staphylococcus aureus adherence to fibrinogen, fibronectin, platelets and endothelial cells under static and flow conditions.

In the present study, the adherence of Staphylococcus aureus (strain 83254) and its RNAIII mutant (WA400) to immobilised fibrinogen and fibronectin, and to human endothelial cells (EC), was studied. [3H]Thymidine-labelled bacteria in stationary phase were incubated on the test surfaces for 20 min under static or flow (200/s) conditions. The results showed: (a) increased adherence of the RNAIII mutant to fibrinogen under static conditions, and decreased adherence of the mutant to fibronectin and EC under both static and flow conditions compared with the parental strain; (b) stronger ability of the mutant compared with the parental strain to induce platelet aggregation in suspension; (c) greater adherence of the parental strain and the mutant to EC pre-treated with platelet-rich plasma compared with platelet-poor plasma, and to EC pre-treated with platelet-poor plasma compared with control; (d) increased adherence of S. aureus to EC pre-treated with PMA-activated platelets and decreased adherence to EC pre-treated with tirofiban, a platelet glycoprotein IIb-IlIa inhibitor, which paralleled with increased adherence of PMA-activated platelets and decreased adherence of glycoprotein IIb-IIIa-blocked platelets to EC in the absence of bacteria; and (e) adherence of the mutant was more sensitive to pre-treatment of EC with plasma and PMA-activated platelets. In conclusion, RNAIII down-regulates S. aureus adherence to fibrinogen under static condition and up-regulates S. aureus adherence to fibronectin and EC under both static and flow conditions. The potentiating role of activated platelets in the presence of plasma in S. aureus adherence to EC is down-regulated by RNAIII, probably due to down-regulation of adherence to fibrinogen, the important plasma protein bridging S. aureus, platelets and EC.