History of probiotic research

At the end of the 19th century, one school of thought held that ill health began in the colon, through a process of "auto-intoxication". Waste products and toxins from the colon seeped into the bloodstream and initiated the diseases of old age. Reducing putrefaction in the colon became a goal of some therapies, such as dietary regimens.

The fermenting of meat into sausage using lactic acid bacteria preserves the meat against spoilage. These bacteria, which are harmless to the GI tract of man, might benefit him by reducing putrefaction in the gi tract, or so the theory went.

Lactobacilli as probiotics

Lactobacilli have been shown to be present in the GI tract of most healthy humans. They are non-pathogenic, and have been used in sausage-making and other fermented foods for centuries. They lower the pH of their environment by converting sugar to lactic acid, which inhibits the growth of some pathogens.

Lactobacilli were the first genus of bacteria suspected to have health benefits, rather than to be agents of disease. Lactobacillus acidophilus, found in yogurt, was believed to be responsible for the longevity of some eastern Europeans who traditionally consumed it as a staple food. This supported the argument that lactobacilli had a positive effect on human health.

Lactobacillus acidophilus was used in the form of acidophilus milk to treat constipation and diarrhea in the 1920s and 1930s in the USA. It was widely administered, often with positive results¹. Commercial acidophilus tablets were marketed, but they were decried by serious researchers for their lack of any viable L. acidophilus bacteria. When the public derived no benefits from the inert "acidophilus tablets", interest waned.

Lactobacillus acidophilus has been used in three human studies to reduce candida populations in the GI tract^2,3,4. They showed positive results, but were small and not part of a coordinated research effort.

Antibiotics

The advent of antibiotics resulted in a renewed interest in the gastrointestinal microflora. The GI side-effects common to antibiotic treatment were felt to be due to their destruction of this microflora. This appeared to reduce a patient's resistance to GI infection by organisms resistant to the antibiotic.

If the natural, protective microflora could be supplemented orally, perhaps it would buttress the patient against some of these GI side-effects. Lactobacillus acidophilus was used in medical research as far back as the 1950s in an effort to prevent the destructive effect of antibiotics⁵.

Screening for probiotic attributes

Different species of lactobacilli have markedly different characteristics. Recent trials treating GI disturbances(i.e. traveler's diarrhea, constipation) with different strains of lactobacilli produced mixed results. Strain selection is important. The strain used should have the following attributes for it to implant and have a beneficial effect^{6, 7}:

1. Adhere to the mucosal surface of the GI tract (to prevent being washed out by peristalsis).
2. Produce metabolites inhibitory or antagonistic to the indigenous microflora (to improve it's chance of becoming established in the gut).
3. Survive the rigors of transit through the GI tract (such as exposure to stomach and bile acids).
4. Poses antagonism towards a particular, target pathogen.

References

1. Kopeloff N. "Lactobacillus Acidophilus" Williams and Wilkins Co., 1926
2. Tomada T and Nakano Y "Variations in intestinal candida populations in patients receiving antileukemic therapy" Bulletin of the Osaka Medical School 30(1):14-18, 1984
3. Tomada T et al. "Intestinal Candida overgrowth and Candida infection in patients with leukemia: effect of Bifidobacterium administration" Bifidobacteria Microflora 7(2):71-74,1988
4. Lidbeck A et al. "Impact of Lactobacillus acidophilus on the normal intestinal microflora after the administration of two antimicrobial agents" Infection 16(6):329-336, 1988
5. Gordon D. et al. "A Lactobacillus preparation for use with antibiotics" Lancet May 4, 1957, pp899-901
6. Conway P.L. and Henriksson A. "Strategies for the isolation and characterization of functional probiotics" in: Human Health: The Contribution of Microorganisms, Springer-Verlag, 1994
7. Fuller R. "Probiotics in human medicine" Gut 32:439-442, 1991

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