Vibrio cholera and stomach acidity reproduced from

Info iconThis preview shows page 1. Sign up to view the full content.

View Full Document Right Arrow Icon
This is the end of the preview. Sign up to access the rest of the document.

Unformatted text preview: cer. Vibrio cholera and stomach acidity (Reproduced from Microbiology: An Evolving Science, 2009 by Slonczewski and Foster) We have known for a hundred years that the stomach contents are acidic and that gastric acidity can kill bacteria. Just how important that acidity is for protection against microbes is illustrated by the infection caused by Vibrio cholerae, the causative agent of cholera. Cholera is a severe diarrheal disease endemic to many of the poorer countries of the world. The toxin produced by the organism acts on the intestinal lining to cause voluminous diarrhea—as much as 10 liters a day. Death can occur rapidly as a result of dehydration and shock. Although cholera actually affects the intestines, not the stomach, the bacteria must survive passage through the stomach to reach the intestines. In the middle of the last century, the U.S. government was concerned that troops dispatched to endemic countries could develop cholera and become incapacitated in large numbers, so the U.S. Army decided to test potential cholera vaccines for their efficacy. The vaccines were living cultures of genetically weakened cholera bacteria that could not cause serious disease. Living strains were preferred because they were expected to grow in the gastrointestinal tract and stimulate natural mucosal immunity). But after administration of huge numbers of virulent organisms to healthy volunteers (as a control group), very few contracted cholera. This was confusing because hundreds of thousands of malnourished people in India easily contract the disease. Why did volunteers given live cholera generally fail to develop the disease? Variations in resistance to cholera were discovered to be related to differences in stomach acidity. The organism V. cholerae is extremely sensitive to low pH; even a pH of 4 will readily kill it. Because the pH in the stomachs of healthy volunteers was well below 4, it easily killed V. cholerae. Malnourished people, however, suffer from achlorhydria (loss of stomach acid). This permissive environment gives ingested microbes time to enter the less acidic intestine, where they can thrive and cause disease. Cholera epidemics in which thousands of people die, even today, typically occur among poor, malnourished populations. Because the U.S. populace is better nourished, cholera is not a major problem in the United States. The intestinal tract Small intestine The gastrointestinal tract beyond the stomach consists of an extremely long tube made of several sections, each of which provides a uniquely different environment that supports the growth of different bacterial and archaeal species. Overall there are about 1013 to 1014 prokaryotic organisms in the entire gastrointestinal tract with the vast majority located in the large intestine. The upper part of the small intestine adjacent to the stomach is fairly acidic and resembles the stomach in its natural flora. Moving downward, the pH gradually becomes less acidic and bacterial numbers incre...
View Full Document

This note was uploaded on 10/25/2013 for the course MICB 201 taught by Professor Davidturner during the Fall '12 term at UBC.

Ask a homework question - tutors are online