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Vibrio cholera and stomach acidity
(Reproduced from Microbiology: An Evolving Science, 2009 by Slonczewski and
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...
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This note was uploaded on 10/25/2013 for the course MICB 201 taught by Professor Davidturner during the Fall '12 term at UBC.
- Fall '12