Bacterial adhesion to surface hydrophilic and hydrophobic contact lenses

The aim of this paper was to determine the adhesion of two physico-chemically characterized bacterial strains to a surface hydrophilic (CL A, water contact angle 57 degrees) and hydrophobic (CL B, water contact angle 106 degrees) hydrogel contact lens (CL) with and without an adsorbed tear film in a parallel plate flow chamber. Hydrophobicity (by water contact angles), charge (by particulate microelectrophoresis) and elemental composition (by XPS) of the surfaces of seven bacterial strains were characterized, after which two strains were selected for further studies. On CL surfaces, hydrophobicity, elemental composition, and mean surface roughness (by AFM) were determined, as well as the protein composition of tear films adsorbed on these lenses (by sodium dodecylsulphate-polyacrylamide gel electrophoresis (SDS-PAGE)). Bacterial cell surfaces were relatively uncharged and water contact angles on lawns of different strains ranged from hydrophobic to hydrophilic. After adsorption of tear film components, N/C elemental surface concentrations increased on CL A and CL B and differences in water contact angles between both lenses reduced to range from 57 degrees (CL A) to 69 degrees (CL B). However, different protein compositions were inferred. The surface roughness of CL A increased from 4 to 13 nm. while it remained 16 nm for CL B. Adhesion of hydrophobic Pseudomonas aeruginosa #3 was more extensive than of hydrophilic Staphylococcus aureus 799, with no differences between both lenses. The hydrophobicity of P. aeruginosa #3 after cell surface damage decreased and its adhesion was reduced on CL A and strongly on CL B. In addition, passage of an air-liquid interface yielded more detachment of S. aureus 799 than of P. aeruginosa #3 from the CL surfaces. In conclusion, the hydrophobicity of CL surfaces dictates the composition of the adsorbed tear film and therewith plays an important role in bacterial adhesion to lenses. Adhesion of hydrophobic P. aeruginosa #3 was more tenacious than of hydrophilic S. aureus 799.