Poly(ethylene oxide) (PEO)-brushes are generally recognized as protein-repellent surfaces, and although a role in discouraging microbial adhesion has been established for some strains and species, no study exists on the effects of PEO-brushes on a large variety of bacterial and yeast strains. In this paper, a PEO-brush has been covalently attached to glass and silica by reaction in a polymer melt. Subsequently, the presence of a PEO-brush was demonstrated using contact angle measurements, X-ray photoelectron spectroscopy and ellipsometry. For five bacterial (Staphylococcus epidermidis, Staphylococcus aureus, Streptococcus salivarius, Escherichia coli and Pseudomonas aeruginosa) and two yeast strains (Candida albicans and Candida tropicalis), adhesion to PEO-brushes was compared with adhesion to bare glass in a parallel plate flow chamber. The initial deposition rates of Sta. epidermidis, Sta. aureus and Str. salivarius to glass were relatively high, between 2400 and 2600 cm "2 s "1 , while E. coli and P. aeruginosa deposited much more slowly. The initial deposition rates of the yeasts to glass were 144 and 444 cm "2 s "1 for C. albicans GB 1/2 and C. tropicalis GB 9/9, respectively. Coating of the glass surface with a PEO-brush yielded more than 98 % reduction in bacterial adhesion, although for the more hydrophobic P. aeruginosa a smaller reduction was observed. For both yeast species adhesion suppression was less effective than for the bacteria and here too the more hydrophobic C. tropicalis showed less reduction than the more hydrophilic C. albicans. The PEO-brush had a thickness of 22 nm in water, as inferred from ellipsometry. Assuming that on bare glass the adhered micro-organisms are positioned only a few nanometers away from the surface and that the brush keeps them at a distance of 22 nm, it is calculated that the brush yields a sevenfold attenuation of the Lifshitz-Van der Waals attraction to the surface between the micro-organisms and the surface. Decreased Lifshitz-van der Waals attraction may be responsible for the suppression of the microbial adhesion observed.

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Abstract-Poly(ethylene oxide) brushes have been covalently bound to glass surfaces and their presence was demonstrated by an increase in water contact angles from fully wettable on glass to advancing contact angles of 54 ± , with a hysteresis of 32 ± . In addition, electrophoretic mobilities of glass and brush-coated glass were determined using streaming potential measurements. The dependence of the electrophoretic mobilities on the ionic strength was analyzed in terms of a softlayer model, yielding an electrophoretic softness and xed charge density of the layer. Brush-coated glass could be distinguished from glass by a 2-3-fold decrease in xed charge density, while both surfaces were about equally soft. Adhesion of Staphylococcus epidermidis HBH276 to glass in a parallel plate ow chamber was extremely high and after 4 h, 19:0 £ 10 6 bacteria were adhering per cm 2 . In contrast, the organisms did not adhere to brush-coated glass, with numbers below the detection limit, i.e. 0:1 £ 10 6 per cm 2 . These results attest to the great potential of polymer brushes in preventing bacterial adhesion to surfaces.

Bacteria adhering to surfaces demonstrate random, nanoscopic vibrations around their equilibrium positions. This paper compares vibrational amplitudes of bacteria adhering to glass. Spring constants of the bond are derived from vibrational amplitudes and related to the electrophoretic softness of the cell surfaces and dissipation shifts measured upon bacterial adhesion in a quartz-crystal-microbalance (QCM-D). Experiments were conducted with six bacterial strains with pairwise differences in cell surface characteristics. Vibrational amplitudes were highest in low ionic strength suspensions. Under fluid flow, vibrational amplitudes were lower in the direction of flow than perpendicular to it because stretching of cell surface polymers in the direction of flow causes stiffening of the polyelectrolyte network surrounding a bacterium. Under static conditions (0.57 mM), vibrational amplitudes of fibrillated Streptococcus salivarius HB7 (145 nm) were higher than that of a bald mutant HB-C12 (76 nm). Amplitudes of moderately extracellular polymeric substance (EPS) producing Staphylococcus epidermidis ATCC35983 (47 nm) were more than twice the amplitudes of strongly EPS producing S. epidermidis ATCC35984 (21 nm). No differences were found between Staphylococcus aureus strains differing in membrane cross-linking. High vibrational amplitudes corresponded with low dissipation shifts in QCM-D. In streptococci, the polyelectrolyte network surrounding a bacterium is formed by fibrillar surface appendages and spring constants derived from vibrational amplitudes decreased with increasing fibrillar density. In staphylococci, EPS constitutes the main network component, and larger amounts of EPS yielded higher spring constants. Spring constants increased with increasing ionic strength and strains with smaller electrophoretically derived bacterial cell surface softnesses possessed the highest spring constants.

Adhesion and residence-time-dependent desorption of two Staphylococcus aureus strains with and without fibronectin (Fn) binding proteins (FnBPs) on Fn-coated glass were compared under flow conditions. To obtain a better understanding of the role of Fn-FnBP binding, the adsorption enthalpies of Fn with staphylococcal cell surfaces were determined using isothermal titration calorimetry (ITC). Interaction forces between staphylococci and Fn coatings were measured using atomic force microscopy (AFM). The strain with FnBPs adhered faster and initially stronger to an Fn coating than the strain without FnBPs, and its Fn adsorption enthalpies were higher. The initial desorption was high for both strains but decreased substantially within 2 s. These time scales of staphylococcal bond ageing were confirmed by AFM adhesion force measurement. After exposure of either Fn coating or staphylococcal cell surfaces to bovine serum albumin (BSA), the adhesion of both strains to Fn coatings was reduced, suggesting that BSA suppresses not only nonspecific but also specific Fn-FnBP interactions. Adhesion forces and adsorption enthalpies were only slightly affected by BSA adsorption. This implies that under the mild contact conditions of convective diffusion in a flow chamber, adsorbed BSA prevents specific interactions but does allow forced Fn-FnBP binding during AFM or stirring in ITC. The bond strength energies calculated from retraction force-distance curves from AFM were orders of magnitude higher than those calculated from desorption data, confirming that a penetrating Fn-coated AFM tip probes multiple adhesins in the outermost cell surface that remain hidden during mild landing of an organism on an Fn-coated substratum, like that during convective diffusional flow.Staphylococcus aureus is a versatile pathogen which can adhere to epithelial cells, endothelial cells, and fibroblasts, as well as to plasma-exposed biomaterial implant surfaces in the human body (12), causing potentially persistent infections. The best-described mechanism of S. aureus adhesion to eukaryotic cells and other fibronectin ( At constant temperature and pressure, bacterial adhesion to surfaces is accompanied by a decrease in the Gibbs energy (⌬G). ⌬G is composed of a change in enthalpy (⌬H) and a change in entropy (⌬S) according to the following equation:where T is the temperature (in Kelvin). The enthalpy tends to reach a minimum value, whereas the entropy strives for a maximum value. The change in enthalpy can be determined by determining the heat exchange between a system and its environment, while direct determination of the entropy is practically impossible. Many biological processes are characterized by strong enthalpy-entropy compensation (10); that is, they occur spontaneously by virtue of an increase in entropy that compensates for an unfavorable enthalpy effect or vice versa. The enthalpy of the interaction between bacterial cell surfaces and proteins can be assessed using isothermal titration calorimetry (ITC). Xu et al. (28) determined the adso...

Advances in medical research has resulted in successful treatment of many life-threatening infectious diseases as well as autoimmune and lifestyle-related diseases, increasing life-expectancy of both the developed and developing world. As a result of a growing ageing population, the focus has also turned on chronic diseases which seriously affect the quality of older patient life. Xerostomia (dry mouth) is one such condition, which leads to bad oral health and difficulty in consumption of dry foods and speech. Saliva substitutes are used to ease symptoms. However, they often don’t work properly and objective comparison of saliva substitutes to mimic natural salivary functions does not exist. The study thus aims to develop an ex vivo friction assay simulating dry mouth conditions and facilitating objective comparison of saliva substitutes. A reciprocating sliding tongue-enamel system was developed and compared to a PDMS (polydimethylsiloxane)-PDMS friction system. The tongue-enamel system, but not the PDMS-PDMS model, showed high mucin-containing saliva (unstimulated and submandibular/sublingual saliva) to give higher Relief than mucin-poor lubricants (water, parotid saliva, Dentaid Xeros) and correlated well (r = 0.97) with in vivo mouth feel. The tongue-enamel friction system mimicked dry mouth conditions and relief and seems suited to test agents meant to lubricate desiccated oral surfaces.

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