Microbial keratitis from the bacterium Pseudomonas aeruginosa (PA) is a serious eye infection associated with soft contact lens (SCL) wear. We study the kinetics of PA adherence on several commercial SCL for two different PA strains (PAK, and PAK FliC^-.) differing in the presence or absence of a flagellum. To mimic on-eye contact lens wear, the lens is mounted with its posterior side exposed to a laminar flow field at a fixed shear rate of 0.4 s^-1 (characteristic of blinking). Viable cell counts quantify how many bacteria irreversibly attach to the SCL.

The amount of adhered bacteria increases linearly with flow time for all lenses, bacteria concentrations, and strains. After 2 h exposure to 10⁷cfu/ml in nutrient-free PBS, typical adherence densities for PAK are on the order of 10³ cfu/mm² for all lens types. Levéque theory successfully describes the bacterial uptake kinetics. Diffusivity of the PAK FliC^- non-flagellum strain is orders of magnitude smaller that that of PAK as verified by diffusion coefficient measurements using the restricted diffusion cell technique. Hence, convective-diffusion explains the 10³x higher adsorption of PAK vs. PAK FliC^-. We conclude that determination of adherence kinetics of bacteria on SCLs must account for mass transfer resistances. Therefore diffusion coefficients for the various bacterial strains must be measured.