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

Abstract

A b s t r a c tThe influence of the shear stress (rw) under which biofilms were formed was assessed on their susceptibility to removal when exposed to chemical and mechanical stresses. A rotating cylinder reactor was used to form biofilms, allowing the simulation of rw conditions similar to those found in industrial settings, particularly in areas with low rw like elbows, corners, valves and dead zones. Bacillus cereus was used as a model bacterium for biofilm formation.Biofilms were formed on AISI316 stainless steel cylinders under different rw (estimated at 0.02, 0.12 and 0.17 Pa) for 7 days. Some phenotypic characteristics, including thickness, biomass production, cellular density and extracellular proteins and polysaccharides content were assessed. Biofilm density was found to increase significantly with rw while the thickness decreased. Also, biofilms formed at 0.02 Pa had lowest biomass content, cell density and extracellular polysaccharide content. Those characteristics were not statistically different for the biofilms formed under 0.12 and 0.17 Pa.Ex situ tests were performed by treating the biofilms with the biocide benzyldimethyldodecyl ammonium chloride (BDMDAC), followed by exposure to increasing rw conditions, up to 1.84 Pa (whereas the maximum rw used during growth was 0.17 Pa). The biofilms formed under low rw were more resistant to removal caused by the BDMDAC action alone. Those formed under higher rw 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 0.17Pa. 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. IntroductionThere is a lack of efficient strategies to clean stagnant zones in industrial plants (Brooks and Flint, 2008). Crevices, corners, dead zones, valves or areas where the mixing rate is low are almost inevitable. Stagnation promotes bacterial accumulation, ultimately leading to biofouling (Manuel et al., 2010). Biofouling is a damaging problem, affecting the energetic efficiency of industrial processes, causing corrosion of the surfaces, decreasing product quality and eventually promoting the spread of pathogens and resistant infectious diseases (Costerton et al., 1999;Ludensky, 2003;Srey et al., 2013). In industrial settings, surface disinfection is usually focused on the use of biocides, aiming to inactivate the microorganisms (Cloete et al., 1998;Faille et al., 2013). Since biofilms are complex biological structures adhered to a sur-face, these strategies often fail, as the removal of biomass is neglected. Hence, cleaning the biomass from the surfaces is fundamental for controlling biofilm development (Flemming, 2011).In the biofilm formation process, the hydrodynamic conditions define the transport of the cells, oxyg...

Mechanosensing of shear by Pseudomonas aeruginosa leads to increased levels of the cyclic-di-GMP signal initiating biofilm development

“…We have shown that PAO1 can respond to shear stresses on the order of millipascals. The shear stresses and rates we apply are 2-100 times smaller than stresses commonly studied for biofilm formation or found in host physiology (34)(35)(36). This suggests that PAO1 and other bacteria may be remarkably sensitive to mechanical stresses in their environment.…”

“…Our work also suggests that the mechanical stresses from the environment, such as shear stress by external flow, to which bacteria are subjected in early biofilm initiation, may impact properties of the mature biofilm. For several bacterial species, biofilms that are grown under high shear are more elastic and denser in matrix proteins and EPS than biofilms grown under low shear (34,35,46). Thus, early enhancement in c-di-GMP time course might allow biofilm-forming bacteria to adapt the strength and resilience of the biofilms formed to better resist mechanical removal.…”

Abundance and Distribution of Enteric Bacteria and Viruses in Coastal and Estuarine Sediments—a Review

“…Turbulence generated during peak flow results in mixing, an increase in oxygenation, bubble generation, and shear stress, which increases detachment rates from sediment and is dependent on bacterial shape and strain, and biofilm cohesive strength (Gomez-Suarez et al, 2001; Young, 2006; Lemos et al, 2014; Figure 1D). The release/resuspension of bacteria from biofilms within sediments is dependent on the combination of physicochemical forcing (Walter et al, 2013) and biotic factors, such as grazing and quorum sensing (Costerton et al, 1995; Kim et al, 2016) which could impact particulate loading to the water column (Figure 1E).…”

The antibacterial activity and modes of LI-F type antimicrobial peptides againstBacillus cereus in vitro

“…Establishment of B. cereus biofilms on food processing equipment poses a persistent risk to food safety and public health due to the protective effect that the exopolysaccharide matrix confers against cleaners and sanitizers. There is currently increasing interest in biofilm eradication via mechanical clearance, the development of novel antibiofilm material or new antimicrobial agents (Overhage et al 2008;Chaudhari et al 2012;Lemos et al 2015;Pechook et al 2015).…”