Fig. 4
The effect of exogenous fatty acids on polymyxin B, colistin, and imipenem resistance in Pseudomonas aeruginosa. Bacteria were grown at 37 °C in G56 (pH 7.4) (a-c) or CM9 (d) with and without 300 μM of the indicated fatty acids to mid-log phase (OD = 0.8). Cultures were pelleted, washed with G56 and resuspended in G56or CM9 to an OD600 of 0.1. Fatty acids were added to a final concentration of 300uM. The bacterial suspension was distributed into microtiter plates and two-fold concentrations of polymyxin B, colistin, or imipenem were added. After 20 h incubation at 37 °C, the optical density (600 nm) was read using a Biotek Synergy microplate reader. Experiments were conducted in triplicate, with each value representing the mean and standard deviation. Symbols circled by dotted line indicate significant differences (p < 0.002) as compared to the control (no fatty acid) at the particular antimicrobial concentration