R.S.W.Woodward R.S.W.Woodward at newcastle.ac.uk
Sun Jan 22 11:45:54 EST 1995

Re: the belief that the beneficial action of yoghurt is reliant upon the 
restoration of a beneficial GI community.

I work in avian probiotics so the following may not be of much relevance 
when applied to human physiology but I thought it may be of interest 
anyway. Although the action of probiotic organisms is unknown, the 
following theories have been put forward to explain their beneficial effects:

- Exclusion of pathogens by use of attatchment sites. i.e. attatchment of 
Lactobacilli to gut cell surface receptors via pili/fimbriae.
- Excretion of antimicrobials. 
   Both Lactobacilli and Enterococci produce lactic acid.
   Lactobacilli also prod. antimicrobials known to inhibit the growth of 
Salmonella, Shigella, Staphylococcus, Proteus, Pseudomonas and E.coli. 
(Acidophilin, Acidulin, Lactobacilin & Lactocidin).
   Lactobacilli also prod. other organic acids such as acetic acid and 
hydrogen peroxide which may stimulate the anti-bacterial 
lactoperoxidase-thiocyanate enzyme system in the gut.
- Competition for food. i.e. Enterococcus faecium is able to utilise more 
of the breakdown products of food than can E.coli.
- Detoxification of metabolites.
    Lactobacillus delbrueckii is able to neutralise E.coli endotoxins in vitro.
    In normal metabolism gut bacteria produce enzymes such as 
nitroreducatase, beta glucuronidase, and azoreductase that are considered 
harmful as they catalyse the transformation of food to potential 
carcinogens or toxins, Lactobacilli fed to poultry and pigs results in a 
decreased activity of these enzymes.
    Some Lactobacilli also take up cholesterol.
- Enhanced availability of nutrients and micronutrients to the host?
- Provision of nutrients and growth factors to the beneficial flora?
-Stimulation of local immunity?
Hope this of some interest to you, 
                                  Yours, Beccy Woodward.

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