We demonstrate that the surface motility of the bacterium, Pseudomonas aeruginosa, is hindered by a crystalline hemispherical topography with wavelength in the range of 2-8 μm. The motility was determined by the analysis of time-lapse microscopy images of cells in a flowing growth medium maintained at 37 °C. The net displacement of bacteria over 5 min is much lower on surfaces containing 2-8 μm hemispheres than on flat topography, but displacement on the 1 μm hemispheres is not lower. That is, there is a threshold between 1 and 2 μm for response to the topography. Cells on the 4 μm hemispheres were more likely to travel parallel to the local crystal axis than in other directions. Cells on the 8 μm topography were less likely to travel across the crowns of the hemispheres and were also more likely to make 30°-50° turns than on flat surfaces. These results show that surface topography can act as a significant barrier to surface motility and may therefore hinder surface exploration by bacteria. Because surface exploration can be a part of the process whereby bacteria form colonies and seek nutrients, these results help to elucidate the mechanism by which surface topography hinders biofilm formation.

The objective of this work was to examine whether close-packed spheres of polystyrene (colloidal crystals) could be used to delay the development of biofilms. We examined early stage biofilm formation of Pseudomonas aeruginosa after 2 days on a flat sheet of polystyrene and on the same solid coated in polystyrene spheres of 450 or 1500 nm diameter. All materials were coated in fetal bovine serum to enable comparison of the effects of different surface curvature while maintaining constant surface chemistry. After 2 days, fluorescence imaging showed that the volume of bacterial colonies was much smaller on the 1500 nm colloidal crystals than on the flat film. In addition, electron microscopy showed that the area covered by structures containing more than one layer of bacteria was significantly reduced on both the 450 and 1500 nm colloidal crystals compared to the flat sheet. This provides proof of concept of biofilm inhibition of a pathogen by a simple nonchemical coating that may find future application in reducing the incidence of infections. Even though the density of adhered bacteria on 450 and 1500 nm was similar after 1 day, biofilm formation after 2 days was delayed more on the 1500 nm spheres than on the 450 nm spheres. We also observed that bacteria have preferred adsorption sites on the 1500 nm colloidal crystals and that cell bodies were often separated. This leads us to hypothesize that the greater spacing between favorable sites on the 1500 nm colloidal crystal hindered the early stage biofilm formation by separation of cell bodies.

No abstract

We examined the effect of a crystalline layer of silica particles in the size range 0.5−4 μm 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 μg/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.

Bacteria traverse surfaces as part of colonizing solids, and it is of interest to hinder this motion to potentially thwart infections in humans. Here, we demonstrate that topographical steps hinder the ability of Pseudomonas aeruginosa PAO1 (P. aeruginosa) to traverse a solid–liquid interface. Using time-lapse fluorescence microscopy and image analysis, we analyzed the motion of P. aeruginosa that were challenged with steps ranging in height from 0.4 to 9.0 μm. Bacterial trajectories are sensitive to the height of the step, the curvature of the step face, and the direction of their motion relative to gravity. When the step height is ≥0.9 μm, which is similar to the cell diameter, there is a reduced probability of the cell crossing the step. For those bacteria that do cross a step, there is a time penalty for crossing steps of height 2–3 μm; this height is similar to the length of the bacterium. For higher steps, the bacteria reorient their cell body while traversing the step riser. Our findings elucidate how topography influences the motion of bacteria and informs strategies for hindering bacterial motion at surfaces.