Fig. 5
The effect of exogenous fatty acids on polymyxin B, colistin, and ampicillin resistance in E. coli. Bacteria were grown at 37 °C in CM9 with and without 300 μM of the indicated fatty acids to mid-log phase (OD = 0.8). Cultures were pelleted, washed with CM9 and resuspended in CM9 to an OD600 of 0.12. Fatty acids were again added to a final concentration of 300uM. The bacterial suspension was distributed into microtiter plates and two-fold concentrations of polymyxin B, colistin, or ampicillin were added. After 20 h incubation at 37 °C, the optical density (600 nm) was read using a Biotek Synergy microplate reader. Shown is a representative from two independent experiments conducted in triplicate, with each value representing the mean (all standard deviations < 0.04). Symbols circled by dotted line indicate significant differences (p < 0.002) as compared to the control (no fatty acid) at the particular antimicrobial concentration