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 Pseudomonas fluorescens biofilms, formed on stainless steel under different shear stress (${\mathrm{\tau }}_{\mathrm{w}}$) conditions (1, 2 and 4 Pa), to chemical (benzalkonium chloride – BAC, glutaraldehyde – GLUT and sodium hypochlorite – SHC) and mechanical (20 Pa) treatments (alone and combined). The biofilms formed under different ${\mathrm{\tau }}_{\mathrm{w}}$ showed different structural characteristics. Those formed under a higher ${\mathrm{\tau }}_{\mathrm{w}}$ 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 Pa-generated biofilms.

Graphical Abstract

Keywords:

• Biocide tolerance
• biofilm resilience
• mechanical removal
• rotating cylinder reactor
• shear stress

Disclosure statement

The authors declare no conflict of interest.

Additional information

Funding

This work was financially supported by: Base Funding – UIDB/00511/2020 of the Laboratory for Process Engineering, Environment, Biotechnology and Energy – LEPABE – funded by national funds through the FCT/MCTES (PIDDAC); Projects Biocide_for_Biofilm – PTDC/BII-BTI/30219/2017 – POCI-01-0145-FEDER-030219; Germirrad – POCI-01-0247-FEDER-072237, funded by FEDER funds through COMPETE2020 – Programa Operacional Competitividade e Internacionalização (POCI) and by national funds (PIDDAC) through FCT/MCTES. PRESAGE – Aquatic/0007/2020 – from the programme ERA-NET – European Research Area networks. This study was further supported by the Portuguese Foundation for Science and Technology (FCT) under the scope of the strategic funding of UIDB/04469/2020 unit and BioTecNorte operation (NORTE-01-0145-FEDER-000004) funded by the European Regional Development Fund under the scope of Norte2020 – Programa Operacional Regional do Norte. Anabela Borges and Henrique Sousa thank the Portuguese Foundation for Science and Technology (FCT) for financial support for their work through the Scientific Employment Stimulus – Individual Call – [CEECIND/01261/2017] and through the research grant for a doctoral degree (2020.09538.BD), respectively.