MadSci Network: Microbiology

Re: Beneficial bacteria

Date: Wed Jul 29 14:57:07 1998
Posted By: Chris Yost, PhD Microbiology
Area of science: Microbiology
ID: 901130800.Mi

Hi Carly,

I will address your questions in the same order that they were recieved.

1) In the stomach Lactobacilli can be found; this would include Lactobacillus acidophilus.

In the small intestine both Streptococci and Lactobacilli will be found.

The large intestine contains many varieties of bacteria in very high numbers. In fact the large intestine can be considered as a specialized fermentation vessel. Bacteria found here include: Enterobacteria, Streptococcus faecalis, Bacteroides, Bifidobacterium, Eubacterium, Peptococcus, Peptostreptococcus, Ruminococcus, Clostridia and Lactobacilli. The environment of the large intestine is quite anaerobic and therefore favours obligate anaerobes.

I used Biology of Microorganisms (5th edition) by Brock and Madigan as a resource to answer this question. There is a more recent edition available and it is quite good. You may be able to get it at your nearest university library. Additionally to find out more about the characteristics of these bacteria you could consult Bergey’s Manual, again you will be able to find this at your nearest university library.

2) Stomach pH is very low indeed, around pH 2. Some bacteria are found on the lining of the stomach, Lactobacillus acidophilus would probably be one such bacterium. Some Lactobacilli can tolerate very low pH conditions. Addtionally, if the bacteria can move down the lining of the stomach it will be protected somewhat by the mucosal surface of the stomach.

Regarding experiments on the movements of bacteria in the GI tract, I am not sure of any research papers. However you could try using Medline to search for any articles which may describe such tests.

3) Any bacteria that are introduced into the GI tract whether anally or orally, as you refer to in your second question, will have to compete against already established bacterial colonies. The GI tract (especially large intestine) contain large populations of bacteria. These bacteria have already adapted to their specific environment and studies have shown that it is very difficult for newly introduced bacteria to compete against already established bacteria and in most cases the newly introduced bacteria lose and die off. The more closely related the introduced species is to normal flora the better chance for survival.

Interestingly, when antibiotics are taken orally they suppress the growth of normal flora bacteria. This inhibition allows other bacteria to sometimes colonize the GI tract, some being pathogenic. Therefore one of the potential complications of orally administered antibiotics is the possiblity for intestinal distress.

Hope this helps. You certainly asked some interesting questions.

Chris Yost

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