Staphylococcal biofilm formation depends on the transcription factor s B . We further investigated the role of s B in biofilm formation and persistence in vitro and in vivo in a subcutaneous rat model. As expected, expression of all s B operon genes was transiently higher in the first 6 h of biofilm formation compared to planktonic bacteria, concurrent with a temporary upregulation of icaA and aap expression. However, we also observed a second upregulation of sigB expression in biofilm more than 2 days old without upregulation of icaA or aap. Biofilm formation by Staphylococcus epidermidis strains 8400 and 1457 was compared to that of isogenic mutants with inactivation of rsbU, of rsbUVW and of the entire s B operon. Both wild-type strains and the constitutively sigBexpressing rsbUVW mutant showed a strong biofilm-positive phenotype. The rsbUVW mutant biofilm was, however, thinner and more evenly spread than the wild-type biofilm. Inactivation of SigB in the rsbUVWsigB mutant or mutation of the positive regulator RsbU reduced both the number of sessile bacteria and polysaccharide intercellular adhesin (PIA) synthesis. These differences between the wild-types and their respective mutants appeared after 6 h in in vitro biofilms but only after 4 days in in vivo biofilms. Our results provide additional evidence for a role for s B in biofilm formation. They also suggest a role for s B in biofilm maturation and stability that is independent of PIA or accumulation-associated protein (Aap) and point to significant differences in the temporal development between in vitro and in vivo biofilms.

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Background: Different gene expression patterns correlate with the altered phenotype in biofilmassociated bacteria. Iron and iron-linked genes are thought to play a key-role in biofilm formation. The expression of Fe-linked genes (sirR, sitABC operon) in Staphylococcus epidermidis, was compared in planktonic versus sessile bacteria in vitro and in vivo in a subcutaneous foreign body rat model.

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