Bacterial factors influencing adhesion of Pseudomonas aeruginosa strains to a poly(ethylene oxide) brush.

Most bacterial strains adhere poorly to poly(ethylene oxide) (PEO)-brush coatings, with the exception of a Pseudomonas aeruginosa strain. The aim of this study was to find factors determining whether P. aeruginosa strains do or do not adhere to a PEO-brush coating in a parallel plate flow chamber. On the basis of their adhesion, a distinction could be made between three adhesive and three non-adhesive strains of P. aeruginosa, while bacterial motilities and zeta potentials were comparable for all six strains. However, water contact angles indicated that the adhesive strains were much more hydrophobic than the non-adhesive strains. Furthermore, only adhesive strains released surfactive extracellular substances, which may be engaged in attractive interactions with the PEO chains. Atomic force microscopy showed that the adhesion energy, measured from the retract curves of a bacterial-coated cantilever from a brush coating, was significantly more negative for adhesive strains than for non-adhesive strains (P<0.001). Through surface thermodynamic and extended-DLVO (Derjaguin, Landau, Verwey, Overbeek) analyses, these stronger adhesion energies could be attributed to acid-base interactions. However, the energies of adhesion of all strains to a brush coating were small when compared with their energies of adhesion to a glass surface. Accordingly, even the adhesive P. aeruginosa strains could be easily removed from a PEO-brush coating by the passage of a liquid-air interface. In conclusion, cell surface hydrophobicity and surfactant release are the main factors involved in adhesion of P. aeruginosa strains to PEO-brush coatings.

Stability and effectiveness against bacterial adhesion of poly(ethylene oxide) coatings in biological fluids.

Poly(ethylene oxide) (PEO) coatings have been shown to reduce the adhesion of different microbial strains and species and thus are promising as coatings to prevent biomaterial-centered infection of medical implants. Clinically, however, PEO coatings are not yet applied, as little is known about their stability and effectiveness in biological fluids. In this study, PEO coatings coupled to a glass substratum through silyl ether bonds were exposed for different time intervals to saliva, urine, or phosphate-buffered saline (PBS) as a reference at 37 degrees C. After exposure, the effectiveness of the coatings against bacterial adhesion was assessed in a parallel plate flow chamber. The coatings appeared effective against Staphylococcus epidermidis adhesion for 24, 48, and 0.5 h in PBS, urine, and saliva, respectively. Using XPS and contact-angle measurements, the variations in effectiveness could be attributed to conditioning film formation. The overall short stability results from hydrolysis of the coupling of the PEO chains to the substratum.

Microbial adhesion to poly(ethylene oxide) brushes: influence of polymer chain length and temperature.

Glass surfaces were modified by end-grafting poly(ethylene oxide) (PEO) chains having molecular weights of 526, 2000, or 9800 Da. Characterization using water contact angles, ellipsometry, and X-ray photoelectron spectroscopy confirmed the presence of the PEO brushes on the surface with estimated lengths in water of 2.8-, 7.5-, and 23.7-nm, respectively. Adhesion of two bacterial (Staphylococcus epidermidis and Pseudomonas aeruginosa) and two yeast (Candida albicans and Candida tropicalis) strains to these brushes was studied and compared to their adhesion to bare glass. For the bacterium P. aeruginosa and the yeast C. tropicalis, adhesion to the 2.8-nm brush was comparable to their adhesion on bare glass, whereas adhesion to the 7.5- and 23.7-nm brushes was greatly reduced. For S. epidermidis, adhesion was only slightly higher to the 2.8-nm brush than that to the longer brushes. Adhesion of the yeast C. albicans to the PEO brushes was lower than that to glass, but no differences in adhesion were found between the three brush lengths. After passage of an air bubble, nearly all microorganisms adhering to a brush were removed, irrespective of brush length, whereas retention of the adhering organisms on glass was much higher. No significant differences were found in adhesion nor retention between experiments conducted at 20 and those conducted at 37 degrees C.

Inhibition of adhesion of yeasts and bacteria by poly(ethylene oxide)-brushes on glass in a parallel plate flow chamber.

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.