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What are Probiotics?

How do probiotics work?

Oral probiotics have been associated with a variety of health benefits by restoring the balance of beneficial intestinal microflora. How might probiotic bacteria accomplish this?^[15]

Many hypotheses have been proposed, and some of these involve "good" bacteria:

• Attaching themselves to the surface of the intestinal wall, increase in numbers and make it more difficult for harmful bacteria to become established
• Competing for nutrients more successfully than less desirable bacteria
• Making the intestines more acidic which harmful bacteria do not tolerate
• Producing bacteriocides (chemicals that discourage or kill other bacteria)
• Affecting the immune system so that it acts correctly. The theory behind probiotic use is that by changing the types of bacteria in the small and large intestine, the immune system will stop reacting incorrectly, any inflammation will cease and the GI tract will recover.^[12]

Dietary sources of beneficial microflora include mother's milk and raw fermented foods such as yogurt and sauerkraut but in these foods the bacterial concentrations are relatively low.^[10][14] It is for this reason that numerous preparations of probiotics have become available with higher concentrations and varying numbers of bacterial species.

Lactobacilli and bifidobacteria are the most commonly used bacteria in probiotic preparations. Lactobacillus acidophilus is the most commonly used species, often as a single-strain probiotic. Streptococcus salivarius ssp. thermophilus is also common in probiotic preparations.

The strains of bacteria used must be able to survive gastric acidity, adhere to the intestinal epithelial cells, and at least temporarily colonize the intestine. Since probiotic bacteria do not permanently colonize the host, they need to be ingested on a regular basis to be able to provide continuing benefits.^[13]

It is important to recognise that not all probiotics are equivalent in terms of action and efficacy. Different probiotic preparations have very different bacterial strains and concentrations. Since more than 500 bacterial species are thought to be present in the normal intestine (equivalent to one thousand billion bacteria per gram of colon content), it is very desirable for a probiotic to have a high bacterial count and contain bacteria that have the ability to survive the journey down the GI tract into the colon.^[1][5][13]