Helicobacter pylori:an Emerging Pathogen

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1 Bacteriology at UW-Madison Bacteriology 330 Home Page Helicobacter pylori:an Emerging Pathogen by Karrie Holston, Department of Bacteriology University of Wisconsin-Madison Description of Helicobacter pylori Helicobacter pylori is a spiral-shaped, Gram-negative rod approximately 0.5 x 3.0 micrometers in size. The catalase-positive organism has 4-6 sheathed flagella attached to one pole which allow for motility. History

2 Barry Marshall and Robin Warren of Perth, Western Australia, discovered H. pylori in Originally, the organism was named Campylobacter pyloridis because it was structurally similar to other Campylobacter species, such as C. jejuni. C. jejuni is a gut pathogen which has the ability to colonize the gastric mucosa. C. pyloridis was renamed Campylobacter pylori to fit in with the names of other enteric pathogens. In 1989, it was finally named Helicobacter pylori based on functional and enzymatic properties. Linkage to Gastrointestinal Disease Studies have linked H. pylori to gastrointestinal disease in humans. Even though H. pylori was discovered in 1983, it was noted over 60 years ago that bacteria are associated with damage of the gastric mucosa. H. pylori is the most common cause of gastritis in man. Gastritis is an infiltration of the tissue with lymphocytes and plasma cells. Electron microscopy shows damage to the plasma membrane, vacuolation of the cytoplasm, and ingested bacteria. Gastric epithelial cells acquire features of activated macrophages. Cytokines are produced that attract and activate inflammatory cells. In patients with duodenal ulcers, gastritis is restricted to the antrum. 82 year-old woman with protracted nausea, and occult gastrointestinal bleeding. Endoscopy revealed gastritis involving the gastric fundus (left) and erosive gastritis in the gastric antrum (right). Duodenal ulcers are associated with chronic superficial gastritis in the gastric antrum. Greater than 90% of duodenal ulcer patients are infected with H. pylori. Ulcer patients without H. pylori infection are typically those who have taken non-steroid anti-inflammatory drugs such as aspirin and ibuprofen, which can commonly cause ulcers. The hypothesized route of development

3 of duodenal ulcers is shown in Figure 1 as adapted from Hunt. Figure 1. Postulated Method of Duodenal Ulcer Pathogenesis (Adapted from R.H. Hunt) This proposed method involves an increase in gastrin release caused by H. pylori infection. The increased gastrin level causes increased acid delivery to the duodenum. Ulceration can result from the increased levels of acid. Eradication of the bacterium from a person greatly reduces the recurrence of ulcers. Endoscopy demonstrating two large ulcers in the duodenal bulb, with surrounding duodenitis. There is increased prevalence of H. pylori association with gastric cancer. There is a known stepwise progression from chronic superficial gastritis to intestinal type cancer. It is estimated that H. pylori infection increases the risk of gastric cancer 6 times. There have also been studies of gastric MALT lymphoma which is caused by B-cells stimulated by T-cells stimulated by H. pylori. Research has shown that 5 of 6 early lymphomas regressed after eradication of H. pylori.

4 Endoscopy demonstrating gastric MALT lymphoma. Colonization The antrum of the stomach is a region of moderate acidity where H. pylori usually prefers to colonize first. The bacterium uses its flagella and spiral shape to drill through the mucus layer in the stomach. H. pylori produces adhesins which bind to membraneassociated lipids and carbohydrates. Electron microscopy shows the adherence of H. pylori to plasma membranes of surface epithelial cells. Sometimes an adhesion pedestal is present, which involves tight adhesions associated with local effacement of the microvilli. Adhesins have been identified based on the characterization of bacterial proteins or identification of cellular receptors. Some adhesins and receptors are noted in Table 1 as adapted from Moran. There has been some evidence of tissue tropism in H. pylori colonization. The patterns of tropism are not yet understood, but the classification of adhesins and receptors could lead to an explanation. Table 1. Protein Adhesins Produced by H. pylori and their Corresponding Receptors (Adapted from A.P. Moran) The enzyme urease plays a role in the bacteriumís ability to colonize the acidic gastric environment. The enzyme is found readily on the surface and in the cytoplasm of the bacterium. Urease helps digest urea to produce ammonia and bicarbonate. Ammonia generated around the bacterial cells neutralizes gastric acid. This process benefits the bacterium, but is toxic to gastric epithelial cells. Pathogenicity Ammonia production from urease activity is toxic to mammalian cells. Epithelial cells undergo vacuolation because of urease activity. In addition, urease and other products of H. pylori, including protease, catalase, and phospholipases A2 and C, cause weakening of the mucous bicarbonate layer of the GI tract and damage to surface epithelial cells.

5 LPS seems to inhibit glycosylation of mucus leading to a significant change in the macromolecular structure of mucin from high molecular weight to low molecular weight form. LPS may interfere with protective function of mucus layer and make epithelial cells at the surface vulnerable to acid. LPS from some strains of H. pylori stimulates secretion of pepsinogen. Lastovica et al showed that H. pylori is the only bacterium that stimulates pepsinogen secretion. There are high levels of pepsinogen in ulcer patients. The Lipid A component of LPS in H. pylori has an unusual fatty acid substitution and is under-phosphorylated compared to LPS in other Gram-negative bacteria. Lipid A modifications are known to reduce immunological activity (antigenicity) of LPS. Studies have shown H. pylori does have reduced immunological activity. This lowered activity may allow H. pylori to persist in its host as compared to a more aggressive pathogen. Immune Responses Cultured cells in contact with H. pylori produce Interleukin-8 (IL-8). IL-8 recruits neutrophils and leukocytes by chemotaxis and activates them. IL-8 is stimulated directly by bacterial factors. Cytotoxin is not required for stimulation of IL-8 production. A specific immune response is generated by continued exposure of the bacterium to the gastric mucosa. Almost all patients with chronic gastritis have a specific response to H. pylori by the gastric mucosal IgA. IgG plasma cells are increased with gastritis. Almost all infected patients have IgG antibodies in the serum. A systemic IgA response may be found in some people, but measuring these antibodies is not a reliable method of diagnosis. Prevalence in Humans The prevalence of H. pylori infection in humans correlates with socioeconomic status and age. Low socioeconomic status predisposes to infection. In Western countries, about 50% of people over 60 years of age are infected, while 20% below the age of 40 are infected. Infection is uncommon in young children, but in developing countries, infection does occur in young children. Most adults are infected in developing countries also. H. pylori can be cultured from the stools of most infected people. Although the actual mode of transmission has not been determined, the ability to culture the bacterium from stool is supporting evidence for an oral-fecal mode of transmission. Diagnosis Invasive diagnosis requires endoscopy of a patient, during which biopsies are taken from multiple sites in the esophagus, stomach, and duodenum. The most popular test is the biopsy urease test. This test checks for the presence of the enzyme urease in the biopsy tissue sample. A Gram stain of a biopsy sample can be made. The Giemsa stain can also be used for detection of the organism. A biopsy also allows for a bacteriological culture of the sample. A culture allows for the determination of antibiotic sensitivity.

6 Giemsa stain demonstrating colonization of the gastric mucosa by H. pylori. Noninvasive diagnosis can be made in conjunction with a biopsy test to support findings or confirm eradication after treatment. One method of noninvasive testing is the urease breath test. The entire stomach is sampled with this test. The patient drinks a solution with C-13 or C-14 labeled urea with a meal. In an infected person, labeled CO2 is detected in the breath which is measured with a beta counter. Other methods of testing include testing for antibodies in serum or saliva of a patient. ELISA can be used to measure IgG in serum. Commercial kits have been developed to detect antibodies to H. pylori in the saliva. Treatment The goal of treatment of H. pylori infection is complete removal of the organism. At this time, the best treatment is a triple therapy routine including bismuth subcitrate, metronidazole, and either tetracycline HCl or amoxycillin. This does not work for every patient, therefore other combinations have been and are currently being sought to treat H. pylori. The goal is to find the combination with the highest rate of eradication. A follow up test should be done a few weeks after completion of treatment to ensure eradication of the bacteria. Link to the Treatment recommended by Dr. Marshall himself Conclusion Helicobacter pylori, discovered in 1983 is an emerging pathogen. Its linkage to gastric diseases will initiate further research for treatment of infected patients. With research we will gain a better understanding of this organism so we can protect ourselves from it. Future directions include the development of an immunization for H. pylori. Work has been done in a mouse model with a feline helicobacter called H. felis. The development of a human vaccine will hopefully be the result of these studies. Immunization development takes time and funding, but it could cause contemporary gastrointestinal diseases to be history. References Calam, J Helicobacter pylori. European Journal of Clinical Investigation 24:

7 Crabtree, J. E Immune and Inflammatory Responses to Helicobacter pylori Infection. Scand J Gastroenterol 215:3-10. Fennerty, M. Brian, MD Helicobacter pylori. Arch Intern Med 154: Hunt, R.H The role of Helicobacter pylori in Pathogenesis: the Spectrum of Clinical Outcomes. Scand J Gastroenterol 220:3-9. Labigne, Agnes and Hilde de Reuse Determinants of Helicobacter pylori Pathogenicity. Infectious Agents and Disease 5: Lastovica, A.J., S. Brown, and G.O. Young The effect of lipopolysaccharide from Helicobacter spp and Campylobacter spp on pepsinogen release by gastric mucosa. Communication at the 8th International Workshop on Campylobacters, Helicobacters, and Related Organisms, Winchester, England. Lee, A Prevention of Helicobacter pylori Infection. Scand J Gastroenterol 215: Moran, A. P Pathogenic properties of Helicobacter pylori. Scand J Gastroenterol 215: Pezzi, James S., MD and Yih-Fu Shiau, M.D., Ph.D Helicobacter pylori and Gastrointestinal Disease. American Family Physician 52: Stolte, M. and S. Eidt Helicobacter pylori and the Evolution of Gastritis. Scand J Gastroenterol 214: Online. Internet. 4 April Available URL: Online. Internet. 4 April Available URL: Online. Internet. 4 April Available URL: Return to the Bacteriology 330 Home Page