Bacterial biofilms are communities of micro-organisms encased a self-produced extracellular matrix. While they form readily in a nature, biofilm formation in man-made systems have economic and health consequences. Prior research demonstrated that topographical features comprised of uniform, micro-meter sized particles hindered the biofilm formation of Pseudomonas aeruginosa (P. aeruginosa), an opportunistic human pathogen. The goal of the present work is to 1) further develop a potential anti-biofilm coating by improving its robustness and 2) study the mechanism(s) by which surface topography hinders biofilm formation. The robustness of a topographical coating comprised of an array of silica particles is improved by the introduction of silica bridges through a sol-gel reaction. To study the mechanism(s), specifically, we hypothesized that the motion, or surface motility, of P. aeruginosa is hindered by the presence of micro-meter scale obstacles via physical obstruction. To test this, we analyzed the behavior of single P. aeruginosa cells at micron-scale spatial resolutions using time-lapse fluorescence microscopy, image analysis, and particle tracking techniques. We fabricated various types of micron-scale topography with curvature (particle arrays) and recti-linear features (vertical steps) and varied the critical dimension within the range of 0.5 – 10 µm which spans the dimensions of a typical P. aeruginosa cell. We found that there was a threshold feature size of 1-2 µm at which bacterial surface motility is drastically impacted. On positively curved topography (particle arrays), we found that the frequent obstacles reduced the average speed of a bacterium from 6.2 0.3 µm per 5 min on a flat surface to 2.1 0.3 µm per 5 min on an array of 2 µm particles. Furthermore, we observed that bacteria often move in-between particles, suggesting that bacteria have difficulty climbing over tall obstacles. To further investigate P. aeruginosa's ability to cope with topography, we examined the effect of recti-linear features (vertical steps) on surface motility. We found that step heights > 0.9 µm drastically reduced the probability of crossing and that the average speed when approaching the step is reduced by a factor of 2. Interestingly, we find that bacteria have a slight preference to traverse down which is against the direction of gravity in our system. In summary, these results offer insights into how a surface motile bacterium copes with a topographical surface. Our data indicate that the topography of a surface can impede the surface motility of bacterium and thus, may be an important mechanism by which topography prevents biofilm formation. / Doctor of Philosophy / Bacteria and other micro-organisms can grow on surfaces such as medical devices and cause infections. Other examples of where bacteria can grow are on drains and pipes causing clogging, and on the hulls of ships, thus increasing drag. The goal of the current work is to investigate material coatings that resist the attachment and growth of bacteria on surfaces. We demonstrate that changing the roughness of the surface can reduce the number of bacteria found on the surface. More specifically, we have made surfaces covered with spheres that are approximately the same size as a bacterium, about 1 micrometer (10x smaller than the diameter of hair). We find that the spheres act as physical obstacles that block bacteria from moving on a surface. These results suggest that changing the micro-scale geometry of a surface may reduce the rate of infections on medical devices or hinder the growth of bacteria in other systems
| Identifer | oai:union.ndltd.org:VTETD/oai:vtechworks.lib.vt.edu:10919/94628 |
| Date | 17 October 2019 |
| Creators | Chang, Yow-Ren |
| Contributors | Chemical Engineering, Ducker, William A., Falkinham, Joseph O. III, Bortner, Michael J., Davis, Richey M., Weeks, Eric R. |
| Publisher | Virginia Tech |
| Source Sets | Virginia Tech Theses and Dissertation |
| Detected Language | English |
| Type | Dissertation |
| Format | ETD, application/pdf, application/pdf |
| Rights | In Copyright, http://rightsstatements.org/vocab/InC/1.0/ |
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