Cells and culture conditions.

The following microbial strains were used: the Gram-positive bacterium methicillin-resistant Staphylococcus aureus (MRSA) USA 300, Gram-negative bacteria Escherichia coli K-12 (ATCC 33780) and Pseudomonas aeruginosa ATCC 19660 (Xen 5P), and strain CEC 749 of the luciferase-expressing fungal yeast Candida albicans. A colony of bacteria or fungal yeast was suspended in 20 ml of brain heart infusion (BHI) broth for bacteria or yeast extract-peptone-dextrose (YPD) for C. albicans and grown overnight in a shaker incubator (New Brunswick Scientific, Edison, NJ) at 120 rpm under aerobic conditions at 37°C for bacteria and at 30°C for C. albicans. For bacteria, an aliquot of 1 ml from an overnight bacterial suspension was refreshed in fresh BHI for 2 to 3 h at 37°C to mid-log phase. The cell concentration was estimated by measuring the optical density (OD) at 600 nm (OD of 0.6 = 10⁸ cells/ml). The C. albicans cell number was assessed with a hemocytometer and was generally between 10⁷ and 10⁸ cells/ml.