The effects of chemical and mechanical stresses on Bacillus cereus and Pseudomonas fluorescens single- and dual-species biofilm removal

Biofilm control is mainly based on chemical disinfection, without a clear understanding of the role of the biocides and process conditions on biofilm removal. This study aims to understand the effects of a biocide (benzyldimethyldodecyl ammonium chlorideBDMDAC) and mechanical treatment (an increase of shear stress -w) on single- and dual-species biofilms formed by Bacillus cereus and Pseudomonas fluorescens on high-density polyethene (HDPE). BDMDAC effects were initially assessed on bacterial physicochemical properties and initial adhesion ability. Then, mature biofilms were formed on a rotating cylinder reactor (RCR) for 7 days to assess the effects of chemical and mechanical treatments, and the combination of both on biofilm removal. The results demonstrated that the initial adhesion does not predict the formation of mature biofilms. It was observed that the dual-species biofilms were the most susceptible to BDMDAC exposure. The exposure to increasing w emphasised the mechanical stability of biofilms, as lower values of w (1.66 Pa) caused high biofilm erosion and higher w values (17.7 Pa) seem to compress the remaining biofilm. In general, the combination of BDMDAC and the mechanical treatment was synergic in increasing biofilm removal. However, these were insufficient to cause total biofilm removal (100%; an average standard deviation of 11% for the method accuracy should be considered) from HDPE.This work was financially supported by: Base Funding—UIDB/00511/2020 of LEP-ABE funded by national funds through the FCT/MCTES (PIDDAC); Project Biocide_for_Biofilm—TDC/BII-BTI/30219/2017—POCI-01-0145-FEDER-030219; Germirrad—POCI-01-0247-FEDER-072237; pBio4.0—POCI-01-0247-FEDER-033298, funded by FEDER funds through COMPETE2020—Programa Operacional Competitividade e Internacionalização (POCI) and by national funds (PIDDAC) through FCT/MCTES. 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.