The effect of shear stress on the formation and removal of Bacillus cereus biofilms

Ex situ tests were performed by treating the biofilms with the biocide benzyldimethyldodecyl ammonium chloride (BDMDAC), followed by exposure to increasing τw conditions, up to 1.84 Pa (whereas the maximum τw used during growth was 0.17 Pa). The biofilms formed under low τw were more resistant to removal caused by the BDMDAC action alone. Those formed under higher τw were more resistant to the mechanical and the combined chemical and mechanical treatments. The amount of biofilm remaining on the cylinders, after both treatments was statistically similar for biofilms formed under 0.12 and 0.17 Pa. The resistance of biofilms to removal by mechanical treatment (alone and combined with BDMDAC) was related to the amount of matrix polysaccharides. However, none of the methods investigated were able to remove all the biofilm from the cylinders.