Helicobacteriosis (World of Microbiology and Immunology)
Helicobacteriosis is an infection of the gastrointestinal tract that is caused by the Gram-negative, spiral-shaped bacterium called Helicobacter pylori. Ulcers on the lining of the stomach and upper intestinal tract characterize the malady. The ulceration may be a prelude to the development of cancer of the stomach.
Helicobacteriosis is established following the colonization of the stomach by Helicobacter pylori. How the bacteria are transmitted to a person is still unclear. The prevalence of the infection in overcrowded environments, especially where children are present, indicate that person-to-person transmission is most likely, and that personal hygiene plays a role in transmission. Following transmission, the bacterium is able to persist in the extremely acidic environment of the stomach by burrowing under the mucous overlay of the stomach epithelial cells, and because the bacteria produce an enzyme called urease. The enzyme is able to degrade the gastric acid in the stomach.
Helicobacteriosis invariably becomes chronic. Then, the infection can also be referred to as chronic gastritis. The infection can become chronic because initially the infection produces little or no symptoms. Thus, the immune system is not alerted to response to the infection, which provides an opportunity for the bacterial population to become more tenaciously established.
In about 15% of those who become infected, ulcers develop in the stomach or in a region of the upper intestine called the duodenum. The resulting burning feeling caused by increased secretion of acid is relieved by over-the-counter antacids, which can further dissuade people from seeking a physician's care for the malady. If the infection is diagnosed and the bacteria eliminated by antibiotic therapy, the elevated production of acid stops. But, in the absence of treatment, the painful ulcers will recur. Why only fifteen per cent of those who have infections develop ulcers while the other 85% of infected individuals do not is not clear.
Moreover, the molecular basis for the establishment of the ulcers is also still not clear. There has been some indication of toxin involvement. Helicobacter pylori produces a toxin called VacA and a protein called CagA.
More ominously, epidemiologic evidence strongly indicates that Helicobacter pylori stomach infections are associated with the development of various types of stomach cancers. For examples, the bacterial infection is nine times more common in those patients who are diagnosed with cancer of the stomach, and seven times more common in those people who have a tumor of the lymphatic tissue. Studies have demonstrated that even in these advanced cases, the elimination of Helicobacter pylori can produce a shrinking of the tumors.
Helicobacteriosis can be detected in three ways. The first way is by obtaining a sample of stomach tissue. Culturing of the stomach contents on growth media that selects for the growth of Helicobacter pylori over other bacteria is used to isolate the organism. If the region of the stomach where tissue is obtained is free from bacteria, then an infection can be missed.
A second way of detecting the presence of the bacteria is by a breath test. Breathing on a specially prepared support can detect the presence of the urease enzyme that is produced by Helicobacter pylori. Since this enzyme is not commonly produced, the detection of the enzyme is a strong indication of the presence of living bacteria. However, in the absence of the actual isolation of the bacteria, the breath test cannot be absolutely diagnostic.
Finally, antibodies produced in response to a Helicobacter pylori infection can be detected by a blood test.
Once detected, the bacterial infection does respond to antibiotic therapy. Elimination of the infection relieves the symptoms of helicobacteriosis in 80% of those people who are infected.
The discovery that helicobacteriosis has a bacterial origin and the relief of the symptoms upon bacterial eradication has reinforced the validity of a theory that proposes that many chronic and autoimmune diseases, such as certain types of heart disease and rheumatoid arthritis, are caused by an infection by bacteria or other microbe.
See also Bacteria and bacterial infection; Microbial flora of the stomach and gastrointestinal tract