RSF34 1000D and RSF34 4000B growth in high concentrations of polymyxin B is mainly as microcolonies resuspended in the media or adhered to Eppendorf tube walls. Cells were grown for 24 hours in either the vehicle control or polymyxin B (25 μg/ml for RSF34 or 600 μg/ml for all other strains). The OD600 was measured before vortexing and after vortexing (to resuspend microcolonies and growth that was adherent to tube walls). Shown are the means of the ratios of OD600 values post-vortex to pre-vortex for three experiments, with each experiment done in duplicate. Error bars represent the standard errors of the mean. *, Statistically significant difference (p < 0.01) between ratios for growth in the presence of the vehicle control and growth in polymyxin B by unpaired student's t-test.