Preventing bacterial colonization using colloidal crystals

We investigated the adhesion and colony formation of Pseudomonas aeruginosa PAO1 on a solid coated in close-packed spheres of polystyrene. The objective was to determine the effect of surface topography on the early stages of biofilm formation. Solids were pretreated with serum and then exposed to bacteria under low shear for one day in a center for disease control biofilm reactor. Whereas flat sheets are covered in large colonies after one day, a close-packed layer of 630-1550 nm monodisperse spheres prevents colony formation. Moreover, the film of spheres reduces the density of P. aeruginosa adhered to the solid by an average of 80%. Our data show that when P. aeruginosa adheres to the spheres, the distribution is not random. For 630 nm and larger particles, P. aeruginosa tends to position its body in a 2-fold site. We rationalize the selectivity on the basis of energy minimization for adhesion: sites differ in the deformation needed to achieve a given contact area. We rationalize the inhibition of colonization by the 630-1550 nm spheres in terms of the lack of adjacent favorable positions for bacteria. A close-packed layer of polystyrene spheres also delays colony formation on a medical-grade stainless-steel needle over a period of one day. This suggests that a colloidal crystal approach to biofilm inhibition might be applicable to a variety of materials and geometries.