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Mol Microbiol. 2008 Dec;70(6):1540-55. doi: 10.1111/j.1365-2958.2008.06511.x.

Staphylococcus aureus SigB activity promotes a strong fibronectin-bacterium interaction which may sustain host tissue colonization by small-colony variants isolated from cystic fibrosis patients.

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Centre d'Etude et de Valorisation de la Diversité Microbienne, Département de biologie, Faculté des sciences, Université de Sherbrooke, Sherbrooke, QC, J1K 2R1, Canada.


Genes encoding cell-surface proteins regulated by SigB are stably expressed in Staphylococcus aureus small-colony variants (SCVs) isolated from cystic fibrosis (CF) patients. Our hypothesis is that CF-isolated SCVs are locked into a colonization state by sustaining the expression of adhesins such as fibronectin-binding proteins (FnBPs) throughout growth. Force spectroscopy was used to study the fibronectin-FnBPs interaction among strains varying for their SigB activity. The fibronectin-FnBPs interaction was described by a strength of 1000+/-400 pN (pulling rate of 2 microm s(-1)), an energetic barrier width of 0.6+/-0.1 A and an off-rate below 2 x 10(-4) s(-1). A CF-isolated SCV highly expressed fnbA throughout growth and showed a sustained capacity to bind fibronectin, whereas a prototypic strain showed a reduced frequency of fibronectin-binding during the stationary growth phase when its fnbA gene was down-regulated. Reduced expression of fnbA was observed in sigB mutants, which was associated with an overall decrease adhesion to fibronectin. These results suggest that the fibronectin-FnBPs interaction plays a role in the formation of a mechanically resistant adhesion of S. aureus to host tissues and supports the hypothesis that CF-isolated SCVs are locked into a colonization state as a result of a sustained SigB activity.

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