FIG. 4.

Effects of hfq, rpoS, and rpoE-rseABC disruption on biofilm formation by UTI89. The wild-type (WT) UTI89 strain and its derivatives were grown in static M9 medium on flat-bottomed microtiter plates at 37°C for 48 h. Added crystal violet that was retained within wells by bacterial biofilms was eluted into dimethyl sulfoxide. The optical density (A₅₆₂) of this solution correlated with the level of biofilm formation. The graph shows the means for each sample set ± standard deviations, with indicated P values determined by two-tailed unpaired t tests. Of note, planktonic wild-type and mutant bacteria stain equally well with crystal violet in Gram staining assays.