title: Pseudomonas aeruginosa attachment on QCM-D sensors: the role of cell and surface hydrophobicities.
abstract: While biofilms are ubiquitous in nature, the mechanism by which they form is still poorly understood. This study investigated the process by which bacteria deposit and, shortly after, attach irreversibly to surfaces by reorienting to create a stronger interaction, which leads to biofilm formation. A model for attachment of  Pseudomonas aeruginosa  was developed using a quartz crystal microbalance with dissipation monitoring (QCM-D) technology, along with a fluorescent microscope and camera to monitor kinetics of adherence of the cells over time. In this model, the interaction differs depending on the force that dominates between the viscous, inertial, and elastic loads.  P. aeruginosa,  grown to the midexponential growth phase (hydrophilic) and stationary phase (hydrophobic) and two different surfaces, silica (SiO(2)) and polyvinylidene fluoride (PVDF), which are hydrophilic and hydrophobic, respectively, were used to test the model. The bacteria deposited on both of the sensor surfaces, though on the silica surface the cells reached a steady state where there was no net increase in deposition of bacteria, while the quantity of cells depositing on the PVDF surface continued to increase until the end of the experiments. The change in frequency and dissipation per cell were both positive for each overtone (n), except when the cells and surface are both hydrophilic. In the model three factors, specifically, viscous, inertial, and elastic loads, contribute to the change in frequency and dissipation at each overtone when a cell deposits on a sensor. On the basis of the model, hydrophobic cells were shown to form an elastic connection to either surface, with an increase of elasticity at higher overtones. At lower overtones, hydrophilic cells depositing on the hydrophobic surface were shown to also be elastic, but as the overtone increases the connection between the cells and sensor becomes more viscoelastic. In the case of hydrophilic cells interacting with the hydrophilic surface, the connection is viscous at each overtone measured. It could be inferred that the transformation of the viscoelasticity of the cell-surface connection is due to changes in the orientation of the cells to the surface, which allow the bacteria to attach irreversibly and begin biofilm formation.
authors.affiliation: Department of Chemical and Environmental Engineering, University of California-Riverside, Bourns Hall B355, Riverside, California 92521, USA.
authors.forename: Ian M
authors.initials: IM
authors.lastname: Marcus
authors.forename: Moshe
authors.initials: M
authors.lastname: Herzberg
authors.forename: Sharon L
authors.initials: SL
authors.lastname: Walker
authors.forename: Viatcheslav
authors.initials: V
authors.lastname: Freger
mesh_terms: D001422:Bacterial Adhesion; D057927:Hydrophobic and Hydrophilic Interactions; D011145:Polyvinyls / Q000737:chemistry; D011550:Pseudomonas aeruginosa / Q000166:cytology*; D058525:Quartz Crystal Microbalance Techniques; D012822:Silicon Dioxide / Q000737:chemistry; D013499:Surface Properties; D005465:Fluorocarbon Polymers
chemical_list: D011145:Polyvinyls; D012822:Silicon Dioxide; C024865:polyvinylidene fluoride; D005465:Fluorocarbon Polymers