About Me

My name is Angela and I'm a Nursing student at Alverno College. I am currently taking microbiology and learning how microbiology is connected to society. The purpose of this blog is to show how infectious organisms can cause some cancers. Specifically, I will be discussing the relationship between Helicobacter pylori and gastric cancer.

Helicobacter pylori 

Pathologists have been visualizing Helicobacter pylori (H. pylori) for over a century (Wrobiewski, Peek, & Wilson, 2014).  However, it wasn't until three decades ago that Robin Warren and Barry Marshall definitively identified it. The bacteria was identified while culturing an organism from gastric biopsy specimens. In 2005, Warren and Marshall were awarded the Noble Prize of Medicine for discovering H. pylori and its role in peptic ulcer disease.

H. pylori is a spiral shaped, Gram-negative, bacterium that grows in the mucous layer of the human stomach causing chronic inflammation. The shape of H. pylori allows it to burrow into the mucous layer and attach to the cells that line the inner surface of the stomach (National Cancer Institute at the National Institutes of Health, 2013). Once H. pylori is burrowed into the mucous layer it remains there for the lifetime of the host. The mucous layer functions as a defensive mechanism to protect the stomach from digesting itself. H. pylori is able to survive the acidic environment by secreting the enzyme urease. The enzyme converts the chemical urea to ammonia and neutralizes the acidity of the stomach. This makes the environment ideal for bacteria to grow. The ability to colonize in the highly acidic environment interferes with the immune response. The immune cells are unable to reach the stomach lining, making elimination of the bacteria ineffective.    

          

Gastric Cancer 

Every year there are about 1 million cases of gastric cancer diagnosed (Wrobiewski et al., 2014). Gastric cancer is the second leading cause of cancer-related deaths worldwide. Colonization of H. pylori in the lining of the stomach is a main cause of gastric cancer. For many years the relationship between H. pylori and gastric cancer was a debate. However, several studies have been done showing that H. pylori increases the risk of gastric cancer. In 1994, the International Agency for Research on Cancer classified H. pylori as a carcinogen. 

There are two types of gastric cancer. Cancer located at the top inch of the stomach where it meets the esophagus is known as gastric cardia cancer. Non-cardia gastric cancer is known as cancer located in all other areas of the stomach. H. pylori specifically affects non-cardia gastric cancer or cancer of the lower stomach. In some cases, such as cancer of the upper stomach, H. pylori reduces the risk of cancer (Boyles, 2006). The exact reason why H. pylori increases the risk for cancer is unknown.  However, researchers believe the long term presence of inflammation predisposes cells in the stomach lining to become cancerous.   

A needle-like appendage is used in some H. pylori bacteria to inject a toxin into the junctions where cells of the stomach lining meet. The toxin is produced by a gene called cytotoxin-associated gene A (cagA). The toxin, known as CagA, alters the structure of the stomach cells. This allows bacteria to attach more easily. Chronic inflammation is caused by long-term exposure to the toxin. However, not all H. pylori bacteria contain this gene (National Cancer Institute at the National Institutes of Health, 2013).   

   

Connection to Society 

Nearly 2/3 of the world's population harbors H. pylori. However, the infection rate is higher in developing countries than it is in developed countries. H. pylori is usually acquired during childhood and is thought to be spread through contaminated food and water and direct mouth to mouth contact. In Japan, gastric cancer is almost 10-fold higher than rates in the United States. In some regions of the world gastric cancer is the most common malignacny (Wrobliewski et al., 2014).

http://www.liveto110.com/50-of-people-have-h-pylori-infection/

References

Boyles, S. (2006, October). H. pylori has mixed role in cancer. Retrieved from WebMD website: http://www.webmd.com/cancer/news/20061017/h-pylori-has-mixed-role-in-cancer

National Cancer Institute at the National Institutes of Health. (2013, September). Helicobacter pylori and cancer. Retrieved from National Cancer Institute at the National Institutes of Health website: http://www.cancer.gov/cancertopics/factsheet/Risk/h-pylori-cancer

Wroblewski, L. E., Peek, R. M., Jr., & Wilson, K. T. (2014, October). Helicobacter pylori and gastric cancer: Factors that modulate disease risk. Retrieved from American Society for Microbiology website: http://cmr.asm.org/content/23/4/713.full