The Effects of Chemical and Mechanical Stresses on <i>Bacillus cereus</i> and <i>Pseudomonas fluorescens</i> Single- and Dual-Species Biofilm Removal

• Main Authors: Inês B. Gomes, Madalena Lemos, Susana Fernandes, Anabela Borges, Lúcia C. Simões, Manuel Simões
• Format: Article
• Language: English
• Published: MDPI AG 2021-05-01
• Series: Microorganisms
• Subjects: BDMDAC; disinfection; high-density polyethene; shear stress; rotating cylinder reactor
• Online Access: https://www.mdpi.com/2076-2607/9/6/1174

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 chloride—BDMDAC) and mechanical treatment (an increase of shear stress -<inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><msub><mi>τ</mi><mi>w</mi></msub></mrow></semantics></math></inline-formula>) on single- and dual-species biofilms formed by <i>Bacillus cereus</i> and <i>Pseudomonas fluorescens</i> 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 <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><msub><mi>τ</mi><mi>w</mi></msub></mrow></semantics></math></inline-formula> emphasised the mechanical stability of biofilms, as lower values of <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><msub><mi>τ</mi><mi>w</mi></msub><mo> </mo></mrow></semantics></math></inline-formula>(1.66 Pa) caused high biofilm erosion and higher <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><msub><mi>τ</mi><mi>w</mi></msub></mrow></semantics></math></inline-formula> 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.