Figure 2.

Crystal violet biofilm assay of ExPEC strains grown in M9 or 1/2 M9 media. Biofilms were formed in 96-well plates at 28°C for 5 days and quantified by measuring the OD at 630 nm (OD₆₃₀) of dissolved crystal violet. Means and standard error of the mean values of OD₆₃₀ values of 24 replicate wells from three independent cultures are shown. The cutoff OD (ODc) was defined as three standard deviations above the mean OD of the negative control. Biofilm production was classified as follows: OD < ODc = no biofilm production; ODc < OD < 2 × ODc = weak biofilm production; (2 × ODc) < OD < 4 × ODc = moderate biofilm production; and 4 × ODc < OD = strong biofilm production.