FIG. 7.

Cell-free P. aeruginosa stationary-phase culture supernatants but not C₄-HSL inhibit agr expression in S. aureus. (A) Influence of P. aeruginosa culture supernatants (open bars) diluted 1/10, 1/100, or 1/1,000 and staphylococcal AIP-1 at concentrations of 0.27 μM, 0.027 μM, and 0.0027 μM (solid bars) on the expression of agrP3::blaZ. The data are expressed as percent changes compared with the reporter gene fusion exposed to CYGP broth alone. (B) Northern blot analysis of the RNAIII transcript prepared from S. aureus RN6390 grown for 4, 6, or 9 h in the absence of C₄-HSL (lanes 0) or in the presence of C₄-HSL at a concentration of 5 μM (lanes 5) or 15 μM (lanes 15). (C) Dose-response curve showing that C₄-HSL does not inhibit the S. aureus agrP3::blaZ reporter. The error bars indicate standard deviations (n = 3).