Biofilm formation under high shear stress increases resilience to chemical and mechanical challenges

Abstract

The effect that the hydrodynamic conditions under which biofilms are formed has on their persistence is still unknown. This study assessed the behaviour of <i>Pseudomonas fluorescens</i> biofilms, formed on stainless steel under different shear stress (<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msub><mml:mrow><mml:mi>τ</mml:mi></mml:mrow><mml:mrow><mml:mi>w</mml:mi></mml:mrow></mml:msub></mml:math>) conditions (1, 2 and 4<b> </b>Pa), to chemical (benzalkonium chloride - BAC, glutaraldehyde - GLUT and sodium hypochlorite - SHC) and mechanical (20<b> </b>Pa) treatments (alone and combined). The biofilms formed under different <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msub><mml:mrow><mml:mi>τ</mml:mi></mml:mrow><mml:mrow><mml:mi>w</mml:mi></mml:mrow></mml:msub><mml:mi> </mml:mi></mml:math> showed different structural characteristics. Those formed under a higher <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msub><mml:mrow><mml:mi>τ</mml:mi></mml:mrow><mml:mrow><mml:mi>w</mml:mi></mml:mrow></mml:msub></mml:math> were invariably more tolerant to chemical and mechanical stresses. SHC was the biocide which caused the highest biofilm killing and removal, followed by BAC. The sequential exposure to biocides and mechanical stress was found to be insufficient for effective biofilm control. A basal layer containing biofilm cells mostly in a viable state remained on the surface of the cylinders, particularly for the 2 and 4<b> </b>Pa-generated biofilms.