Helicobacter pylori
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Kwame Adu-Wusu |
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Helicobacter pylori is a spiral, gram negative, flagellated, and highly motile bacterium. Transmitted by interpersonal contact, H. pylori is the second most common human bacterial infection and is associated with numerous gastro-intestinal diseases: chronic gastritis, gastric and duodenal ulcers, gastric car-cinoma, and gastric lymphoma. To date, the pathogenesis of H. pylori associated gastrointestinal disease is incompletely understood.
To gain better understanding and insight into H. pylori infection, the Lorenz Lab is utilizing a mouse model. In 1988 a spiral-shaped organism related to H. pylori was isolated from the stomach of a cat and subsequently named Helicobacter felis. H. felis infection in mice resembles H. pylori infection in humans. Gastric inflammation resulting from H. felis infection is characterized by parietal cell loss, intestinal metaplasia, and epithelial hyperplasia, similar to H. pylori-induced disease in humans.
A difficulty that has arisen in using this mouse model is the extreme motility of H. felis. Because the bacterium possesses active flagella, H. felis does not exhibit desired isolated colony growth patterns on standard agar plates. Without individual colony formation, even the simplest of experiments cannot be performed with H. felis. For example, accurate enumeration of bacteria is not possible. Additionally, cloning and other genetic experiments cannot be conducted with H. felis. Consequently, current H. felis studies tend to focus on the infected host disease symptoms rather than microbial pathogenic factors.
Through experimentation, we hope to discover optimal conditions for H. felis colony formation. Our first approach was a series of experiments involving cultivating the bacteria in various concentrations of top agar. It was hypothesized that top agar might restrict the movement of bacteria by providing a matrix whichinhibits microbial motility. Results from preliminary experiments varied, and follow-up trials must be conducted. There was indeed some colony formation, however efficiency is somewhat low. Less than one percent of the bacteria plated formed colonies. The difficulty with cultivating the bacteria in top agar is in spreading the plates evenly, and it is relatively difficult to observe colony formation because the plates become covered with ridges.
Another approach is to modify the pH levels of the agar plates. To thrive in its host, H. felis must protect itself from the acidic environment of the stomach. It was therefore hypothesized that cultivating H. felis at differing pHs may have at least some influence on bacterial growth. Results from these experiments, however, disproved this hypothesis. The plates(pH 5-9) exhibited no colony formation.
Our future experimentation to find optimal conditions for H. felis colony formationwill involve the use of anti-Helicobacter antibodies, agar plates of variable agar and salt concentration, and the development of anti-flagellar antibodies.
Discoveries in this research can in the future lead to improvements in the treatment of and vaccination from Helicobacter infections. Currently natural infection cannot induce an immune response capable of resolving the disease or protecting against future infection. There has been some limited success in mouse immunization and further research will advance the understanding of the human infection.
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Natural Sciences Learning Center
Washington University - Biology
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