Rapid diffusion of fluorescent tracers into Staphylococcus epidermidis biofilms visualized by time lapse microscopy

The transient diffusion of fluorescent tracers into biofilm cell clusters of Staphylococcus epidermidis was visualized by time lapse confocal scanning laser microscopy. Rhodamine B diffused into the center of cell clusters that were 200 to 600 mum in diameter within a few minutes. The apparent effective diffusion coefficient calculated from these data averaged 3.7 X 10(7) cm(2) s(-1) or 11% of the value in pure water. Fluorescein diffused into biofilm more rapidly, with a diffusion coefficient that averaged 1.6 X 10(-6) cm(2) s(-1), or 32% of the value in water. This study provides direct, visual confirmation that solutes the size of many antibiotics and biocides can diffuse rapidly into biofilms.