Induction of fibronectin adhesins in quinolone-resistant Staphylococcus aureus by subinhibitory levels of ciprofloxacin or by sigma B transcription factor activity is mediated by two separate pathways.

We recently reported on the involvement of a RecA-LexA-dependent pathway in the ciprofloxacin-triggered upregulation of fibronectin-binding proteins (FnBPs) by fluoroquinolone-resistant Staphylococcus aureus. The potential additional contribution of the transcription factor sigma B (SigB) to the ciprofloxacin-triggered upregulation of FnBPs was studied in isogenic mutants of fluoroquinolone-resistant strain RA1 (a topoisomerase IV gyrase double mutant of S. aureus NCTC strain 8325), which exhibited widely different levels of SigB activity, as assessed by quantitative reverse transcription-PCR of their respective sigB and SigB-dependent asp23 transcript levels.

A recA-LexA-dependent pathway mediates ciprofloxacin-induced fibronectin binding in Staphylococcus aureus.

Subinhibitory concentrations of ciprofloxacin (CPX) raise the fibronectin-mediated attachment of fluoroquinolone-resistant Staphylococcus aureus by selectively inducing fnbB coding for one of two fibronectin-binding proteins: FnBPB. To identify candidate regulatory pathway(s) linking drug exposure to up-regulation of fnbB, we disrupted the global response regulators agr, sarA, and recA in the highly quinolone-resistant strain RA1. Whereas agr and sarA mutants of RA1 exposed to CPX still displayed increased adhesion to fibronectin, the CPX-triggered response was abolished in the uvs-568 recA mutant, but was restored following complementation with wild type recA.