Controlling Microbial Colonization and Biofilm Formation Using Topographical Cues

Abstract

This dissertation introduces assembly of spherical particles as a novel topography-based anti-biofouling coating. It also provides new insights on the effects of surface topography, especially local curvature, on cell�"surface and cell�"cell interactions during the evolution of biofilms. I investigated the adhesion, colonization, and biofilm formation of the opportunistic human pathogen Pseudomonas aeruginosa on a solid coated in close-packed spheres of polystyrene, using flat polystyrene sheets as a control. The results show that, whereas flat sheets are covered in large clusters after one day, a close-packed layer of 630�"1550 nm monodisperse spheres prevents cluster formation. Moreover, the film of spheres reduces the density of P. aeruginosa adhered to the solid by 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 the confined spaces between particles. After two days, 3D biofilm structures cover much of the flat polystyrene, whereas 3D biofilms rarely occur on a solid with a colloidal crystal coating of 1550 nm spheres. On 450 nm colloidal crystals, the bacterial growth was intermediate between the flat and 1550 nm spheres. The initial preference for P. aeruginosa to adhere to confined spaces is maintained on the second day, even when the cells form clusters: the cells remain in the confined spaces to form non-touching clusters. When the cells do touch, the contact is usually the pole, not the sides of the bacteria. The observations are rationalized based on the potential gains and costs associated with cell-sphere and cell-cell contacts. I concluded that the anti-biofilm property of the colloidal crystals is correlated with the ability to arrange the individual cells. I showed that a colloidal crystal coating delays P. aeruginosa cluster formation on a medical-grade stainless-steel needle. This suggests that a colloidal crystal approach to biofilm inhibition might be applicable to other materials and geometries. The results presented in appendix 1 suggest that colloidal crystals can also delay adhesion of Methicillin resistant staphylococcus aureus (MRSA) while it supports selective adhesion of this bacterium to the confined spaces.