Antibiofilm activity of N-acetylcysteine (NAC) at 8,000 mg/L, colistin (CST), and NAC-CST combinations against three colistin-resistant nonmucoid P. aeruginosa strains in the Nunc-TSP lid system. A potentiation by NAC of colistin antibiofilm activity was observed with all tested strains. CST 8, colistin at 8 mg/L; CST 32, colistin at 32 mg/L. Biofilms not exposed to NAC or CST represent the control. Black lines indicate median values. The x axis is set at the limit of detection (20 CFU/peg).