Shear stress modulates the thickness and architecture of Candida albicans biofilms in a phase-dependent manner

Abstract

Biofilm formation plays an integral role in catheter-associated bloodstream infections caused by Candida albicans. Biofilms formed on catheters placed intravenously are exposed to shear stress caused by blood flow. In this study, we investigated whether shear stress affects the ability of C. albicans to form biofilms. Candida biofilms were formed on catheter discs and exposed to physiological levels of shear stress using a rotating disc system (RDS). Control biofilms were grown under conditions of no flow. Tetrazolium (XTT) assay and dry weight (DW) measurements were used to quantify metabolic activity and biofilm mass respectively. Confocal scanning laser microscopy (CSLM) was used to evaluate architecture and biofilm thickness. After 90 min, cells attached under no-flow exhibited significantly greater XTT activity and DW than those under shear. However, by 24 h, biofilms formed under both conditions had similar XTT activities and DW. Interestingly, thickness of biofilms formed under no-flow was significantly greater after 24 h than of those formed under shear stress, demonstrating that shear exposure results in thinner, but denser biofilms. These studies suggest that biofilm architecture is modulated by shear in a phase-dependent manner.

Figure 1

Effect of shear stress on architecture of catheter-associated Candida biofilms. Panels show orthogonal confocal images of Candida biofilms exposed to (a, c, e) no flow or (b, d, f) shear stress for (a, b) 90 min, (c, d) 6 h, or (e, f) 24 h. Magnification ×20. Arrows indicate side view for each panel, which was used to determine biofilm thickness.

Figure 2

Effect of shear stress on thickness of Candida biofilms grown under no flow (black bars) or shear stress conditions (diagonal hatched bars). Thickness was measured at three dierent places for biofilms grown under no flow or shear conditions for 90 min, 6 or 24 h. Bars represent mean ± SE (n ≥ 3).