Effects of Colloidal Crystals, Antibiotics, and Surface-Bound Antimicrobials on &ITPseudomonas aeruginosa&IT Surface Density

We examined the effect of a crystalline layer of silica particles in the size range 0.5-4 mu m on the adsorption and surface growth of Pseudomonas aeruginosa. Growth on these colloidal crystal monolayers (CCMs) was compared to growth on a flat plate of silica. All surfaces were coated with a thin film of silica to provide chemical uniformity of the different topographies. The results showed that the CCM reduces the density of colony forming units (CFU) on the solid by 99-99.9% when the suspension load was 10(3) CFU. We also examined the interaction between the CCM and either antibiotics or a chemically bound antimicrobial. The addition of 20 mu g/mL tobramycin after an initial 24 h growth period caused a further decrease in CFU counts of about 99-99.9% for all topographies. The percentage reduction as a result of the antibiotics was similar for all topographies, which suggested that there was no particular synergy between the topography and antibiotics. On the other hand, the additive nature of the two effects suggested promise for clinical studies: the large percentage reduction in CFU density on addition of the antibiotic to a flat surface was maintained on the topography, even starting from a much lower CFU density. A similar result was obtained for the combination of CCM and a covalently bound layer of antimicrobial poly(allylamine hydrochloride) (PAH). The PAH reduced the CFU, and the CCM caused a further reduction; the two factors behaved approximately independently. Overall the CCM was found to be very effective at reducing the density of adsorbed P. aeruginosa both with and without the additional reductions caused by antibiotics or surface-bound antimicrobials.