BIOFILM FORMATION IN LAMINAR-FLOW USING PSEUDOMONAS-FLUORESCENS EX101

The relationship between biofilm formation and Reynolds number in laminar flow has been investigated using Pseudomonas fluorescens EX101. It was shown using a Modified Robbins Device that in laminar flow, numbers of viable cells in a developed biofilm increased with Reynolds number (Re 2, 17 and 51.5), as would be expected in a system where molecular transport to the wall is limited by diffusion. By monitoring fluorescent beads in a flowcell with a scanning confocal laser microscope at similar low Reynolds numbers, the velocity profile close to the solid surface was determined. It was shown that the presence of a thin bacterial film (up to 12 mu m) displaced the flow profile away from the wall by a distance equivalent to the film thickness. Total cell counts from the Modified Robbins Device samples were not significantly different at the different flow rates but were higher than viable counts. Interruption of the flow had no significant effect on colonisation by the bacteria through the Modified Robbins Device in the first few hours. However, viable numbers were reduced when the flow was stopped at 7 h after initial colonisation.