Glucose/salt versus plasma requirements for in vitro biofilm formation on stainless steel by different S. aureus strains assessed by SEM at 24 h. Stainless-steel pins were placed in the flow chamber containing TSBGN or TSB + HP media without bacteria, or inoculated with SH1000, UAMS-1, or USA300 S. aureus, and incubated for 24 h at a flow rate of 0.2 ml/min at 37 °C. Afterwards, the pins were harvested and processed for SEM. Representative SEM images of two independent experiments are shown with the region of interest (ROI; red box in the photo) of the biofilm in the left panels obtained at 150x, and at 5000x in the right panels. Of note is that SH1000 produced a greater biofilm in TSBGN that was phenotypically similar to that produced in TSB + HP. In contrast, UAMS-1 failed to produce a biofilm in TSBGN, as evidenced by the sparse cell clusters (black arrows), but generated a robust biofilm containing fibres (white arrows) in TSB + HP. USA300 produced robust biofilms in both media, but fibres (white arrows) were only present when grown in TSB + HP.