Fig. 5.

Cyclo(l-Tyr-l-Pro) and cyclo(l-Phe-l-Pro) antagonize the AIP-mediated activation of the P3 promoter in S. aureus MN8. The P3 promoter from the agr operon was cloned into the lux-reporter vector pGYlux. The AIP-containing supernatant was prepared by growing S. aureus MN8 in BHI medium to the late exponential phase (an OD₆₀₀ of ∼12), removing the cells by centrifugation, and passing the remaining culture supernatant through the 0.45-μm pore-size filter. For each concentration of DKP, increasing concentrations of the AIP-containing S. aureus MN8 supernatant (0–20%, vol/vol) were added, and luminescence was monitored over 12 h.