FIG 1.
Mutation of σB in unrelated biofilm-positive S. aureus strains enhances biofilm formation. (a) Dot blot analysis of PNAG accumulation in different S. aureus strains. Cell surface extracts of biofilm cultures were spotted onto nitrocellulose filters. PNAG production was detected with anti-S. aureus PNAG antiserum. (b) Biofilm formation of the unrelated S. aureus strains and their respective mutants in σB (ΔσB), icaADBC genes (Δica), and ΔσB Δica. Bacteria were grown on polystyrene microtiter plates for 24 h. wt, wild type. (c) Biofilm formation of the wild-type S. aureus strains and their respective σB mutants on polystyrene microtiter plates after 6 h and 24 h. The bacterial cells were stained with crystal violet, and biofilms were quantified by solubilizing the crystal violet with alcohol-acetone and determining the absorbance at 595 nm. The error bars represent the standard deviations of the results of three independent experiments. *, P < 0.05; **, P < 0.01. (d) Colony morphologies of biofilm-positive strains and their isogenic σB mutants on Congo red agar after 24 h of incubation.