Characterization of a modified rotating disk reactor for the cultivation of Staphylococcus epidermidis biofilm

Aims: The purpose of this study was to develop a system that would allow biofilms to be cultivated under strictly defined conditions in terms of dissolved oxygen, fluid shear and to assess whether the method was suitable for the detection of respiratory activity stratification in biofilm samples. Methods: The system is a modified version a commercially available laboratory biofilm reactor and incorporates a number of features such as the provision of defined levels of dissolved oxygen, constant average shear, enhanced gas–liquid mass transfer, aseptic operation and the ability to remove biofilm for ex situ analysis during or after continuous cultivation. Conclusions: The system was shown to be effective for the characterization of the effects of dissolved oxygen on a pure culture of Staphylococcus epidermidis. The versatility of the system offers the potential for cultivating pure culture biofilm in defined, controlled conditions and facilitates a range of analyses that can be performed ex situ. Significance and Impact of the Study: The ability to provide strict regulation of environmental conditions and enhanced transfer of oxygen to the biofilm during cultivation are important, first because oxygen is known to regulate biofilm development in several micro‐organisms and second because many conventional biofilm cultivation systems may not provide adequate oxygen supply to the biofilm.     

Inactivation of Pseudomonas aeruginosa biofilms formed under high shear stress on various hydrophilic and hydrophobic surfaces by a continuous flow of ozonated water

Abstract

The inactivation of Pseudomonas aeruginosa biofilms grown on glass under high shear stress and exposed to a range of dissolved ozone concentrations (2, 5 and 7?ppm) at 10 and 20?min was investigated. The regression equation, log reduction (biofilm)?=?0.64?+?0.59×(C – 2)?+?0.33×(T – 10), described the dependence of biofilm inactivation on the dissolved ozone concentration (C, ppm) and contact time (T, min). The predicted D-values were 11.1, 5.7 and 2.2?min at 2, 5 and 7?ppm, respectively. Inactivation of biofilms grown on various surfaces was tested at a single dissolved ozone concentration of 5?ppm and a single exposure time of 20?min. Biofilms grown on plastic materials showed inactivation results similar to that of biofilms on glass, while biofilms grown on ceramics were statistically significantly more difficult to inactivate, suggesting the importance of utilizing non-porous materials in industrial and clinical settings.     

A rotating disk apparatus for assessing the biodegradation of polycyclic aromatic hydrocarbons transferring from a non-aqueous phase liquid to solutions of surfactant Brij 35

A rotating disk apparatus was used to investigate the biodegradation of PAHs from non-aqueous phase liquids to solutions of Brij 35. The mass transfer of PAHs in absence of surfactant solution was not large enough to replenish the degraded PAHs. The addition of surfactant resulted in an overall enhancement of biodegradation rates compared to that observed in pure aqueous solution. This is because surfactant partition significant amount of PAHs into the bulk phase, where uptake occurs but the supply of PAHs to the aqueous phase through micellar solubilization at latter period limited biodegradation rates. It was demonstrated the relationship between biodegradation rate and surfactant dose and the mechanisms controlling the mass transfer of PAH from NAPLs. The satisfactory comparison of the experimental data with the predictions of a model, which parameters were determined from independent solubilization and dissolution experiments and based on the main assumption that the solutes must be present in the true aqueous phase to be degraded, allows us to conclude the absence of direct uptake of PAHs by bacteria.     

Analysis of the mechanical stability and surface detachment of mature Streptococcus mutans biofilms by applying a range of external shear forces

Well-established biofilms formed by Streptococcus mutans via exopolysaccharide matrix synthesis are firmly attached to tooth surfaces. Enhanced understanding of the physical properties of mature biofilms may lead to improved approaches to detaching or disassembling these highly organized and adhesive structures. Here, the mechanical stability of S. mutans biofilms was investigated by determining their ability to withstand measured applications of shear stress using a custom-built device. The data show that the initial biofilm bulk (~ 50% biomass) was removed after exposure to 0.184 and 0.449 N m^?2 for 67 and 115 h old biofilms. However, removal of the remaining biofilm close to the surface was significantly reduced (vs initial bulk removal) even when shear forces were increased 10-fold. Treatment of biofilms with exopolysaccharide-digesting dextranase substantially compromised their mechanical stability and rigidity, resulting in bulk removal at a shear stress as low as 0.027 N m^?2 and > a two-fold reduction in the storage modulus (G′). The data reveal how incremental increases in shear stress cause distinctive patterns of biofilm detachment, while demonstrating that the exopolysaccharide matrix modulates the resistance of biofilms to mechanical clearance.