| Description |
Gastrointestinal (GI) tracts are the most populated microbial ecosystem in the human body. Microbial undergrowth or overgrowth in the intestine will result in various diseases. One of several bacterial microbiotas that grows in the GI tracts is Helicobacter pylori, which has been prominent topic of study recently. In the first part of dissertation, I investigate how bacteria of the microbiota maintain their population inside the intestine. The outward flow caused by intestinal muscles is continuously evacuating intestine contents including bacteria; however, bacteria manage to keep their population. Some bacteria accomplish this by adhesion to the intestinal wall where there is no flow. However, other bacteria are still able to maintain their population inside the intestine, despite the fact that outward flow is removing them. I investigate different factors that could play a role in maintaining the intestinal microbiota population. The oscillating back and forth flow caused by peristalsis, bacterial reproduction and motility could be important factors in maintaining the bacterial population. In addition, due to the radial variation of axial velocity and diffusion of bacteria, they could axially spread along the intestine (Taylor-Aris dispersion), which would aid population maintenance. I show that combination of peristaltic flow, bacterial motility, and reproduction could not lead to population maintenance. However, enhanced effective diffusion due to Taylor dispersion added to reproduction of bacteria can prevent iv the population from vanishing. In the second part of dissertation, I investigate swimming H. pylori through the mucus gel of stomach. H. pylori is one of the few microorganisms that can thrive in acidic environment of the stomach. It generates ammonia to neutralize the acidic environment around it and turns nearby mucus gel to fluid pocket. The size of fluid pocket is important in describing H. pylori's behavior: in a large zone, swimming occurs as in a fluid through hydrodynamic principles, while in a very small zone the motility could be strongly influenced by nonhydrodynamic cell-mucus interactions including chemistry and adhesion. Here, I calculate the size of the fluid pocket and I find that H. pylori swims through mucus, as if unconfined, in a large pocket of Newtonian fluid. |
