FIG 3.

The normalized tolerance of S. aureus to 500 μM CuSO₄ was determined using a bioassay with and without the addition of spent medium from wild-type P. aeruginosa PAO1 (PaS) or gene deletion or disruption mutants for lasI (a), pchE (b), pqsH (c), or pqsL (d). Spent medium was also prepared with the addition of 50 μM 3-o-C₁₂-HSL to lasI, 50 μM Dha to pchE, 50 μM PQS to pqsH, and 50 μM HQNO to pqsL during and after culturing. A higher concentration (400 μM) of each of the compounds was also added to S. aureus exposed to copper alone during the bioassay. The average and standard deviation from three biological trials with three technical replicates each are plotted. The dashed line represents the copper tolerance of S. aureus alone (SWF).