Effects of cell surface damage on surface properties and adhesion of Pseudomonas aeruginosa

Abstract

Bacterial cell surfaces play a crucial role in their adhesion to surfaces. In the present study, physico-chemical cell surface properties of Pseudomonas aeruginosa, isolated from a case of contact lens associated keratitis, are determined for mid-exponential and early stationary phase cells and for cells after exposure to a lens care solution or after mechanical damage by sonication. Exposure to a lens care solution and mechanical cell surface damage reduced the cell surface hydrophobicity and water contact angles decreased from 129° to 96° and 83°, respectively. Zeta potentials in saline (−9 mV) were hardly affected after mechanical damage, but tri-modal zeta potential distributions, with subpopulation zeta potentials at −11, −28 and −41 mV, were observed after exposure of bacteria to a lens care solution. X-ray photoelectron spectroscopy indicated changes in the amounts of oxygen-, nitrogen- and phosphorus-rich cell surface components. Mid-exponential phase cells had more nitrogen-rich cell surface components than early stationary phase cells, but water contact angles and zeta potentials were not very different. In addition, mid-exponential phase cells adhered better than early stationary phase cells to hydrophobic and hydrophilic substrata in a parallel plate flow chamber. The capacity of P. aeruginosa to adhere was decreased after inflicting cell surface damage. Exposure to a lens care solution yielded a larger reduction in adhesion capacity than sonication, likely because sonication left most of the cells in a viable state, in contrast to exposure to a lens care solution. It is argued that for clinically relevant experiments, it may be preferable to work with surface damaged cells rather than with gently harvested organisms.