In vitro gene expression of sirR (a) and sitC (b) in sessile versus planktonic bacteria. Gene expression is quantified as log10 (cDNA/gDNA) in the y-axis. Time is given in hours in the x-axis. The line that links the data points helps to clarify the results at each time point measured. The error bars represent standard deviations. Fifteen samples from three independent cultures were assessed at each time point. Bacteria were pre-incubated overnight in fRPMI and incubated together with catheter fragments in fRPMI (sessile: dotted line with empty squares; planktonic: dotted line with filled diamonds) or in fRPMI-Fe25 (sessile: full line with crosses; planktonic: full line with empty triangles).