How Probiotics Protect Against Infections

Australian and Japanese scientists may have uncovered the mechanism by which probiotic bacteria protect the gut from E. coli infection.

Over the last few years, scientists have found that lactic acid bacteria and bifidobacteria have health-promoting effects, but until now exactly how they did this wasn’t fully understood.

The human gut is home to a wide variety of microbes that have beneficial effects, including aiding gut function and protecting against illness and infection.

One of these, a probiotic known as Bifidobacterium, modulates host defence responses and protects against infectious diseases.

Lead author, Dr Fukuda of the RIKEN Research Centre for Allergy and Immunobiology in Yokohama, and his team found that a strain of bifidobacterium could protect mice from a strain of Escherichia coli (E. coli). And it was all about the acetate. Let me explain…

Enterohaemorrhagic E. coli (EHEC), produces Shiga toxin, which can cause illness ranging from mild diarrhoea, to much more severe diseases, including haemorrhagic colitis (bleeding of the colon).

In the study, the researchers infected mice with EHEC one week after treating them with one of two strains of bifidobacterium.

Bifidobacterium convert carbohydrates into a range of short chain fatty acids (SFCA). They found that the strain that was best at converting carbohydrates provided the best protection from EHEC.

Therefore the researchers believe acetate improved resistance in the intestinal wall of the mice from Shiga toxin (produced by E. coli), where it normally transfers into the blood stream.

In the past, it was known that acetate made from carbohydrates fermented by bifidobacteria had health benefits, but the researchers say this is the first time anyone had clearly proved it.

This research has helped demonstrate how important these bifidobacteria strains are in maintaining our health.

Dr David Topping, a co-author on the Nature paper, is a Chief Research Scientist with CSIRO Food Futures and Preventative Health Flagships, based in Adelaide. He says that there is a growing understanding of how the gut bacteria work to deliver health benefits.

“Beneficial bacteria exert a wide range of effects through the products of their metabolism of dietary fibre carbohydrates,” he says.

“These products are called short chain fatty acids (SCFA) and this study looked at how one of these acids, acetic acid (acetate), could confer protection against the highly pathogenic E. coli. This bacterium poses a major threat of food-borne infection.”

“The data confirm that acetic acid was critical for survival of infected animals,” he says.

Topping says the study offers promise for the development of more effective prebiotic and probiotic foods to assist in infection control.

But Associate Professor Eiichi Sato, of the Tokyo University of Agriculture, says it may be difficult to apply this experiment directly to humans

“As animals ourselves, we have more than 1000 different kinds of microorganisms living in our guts which produce intestinal biota (bacterial flora) that are largely different from the intestinal biota of a mouse,” he says.

“But bifidobacteria are a well-known strain of probiotics so I think it would be safe to expect that someday someone will be able to clarify our defence mechanism against diseases.”


Emed’s Comment:

Bifidobacterium are natural inhabitants of the colon and they are the first bacteria to colonise the newborn’s gut after birth.

Since they induce a large variety of enzymatic activities, they play a key role in the stimulation of the immune system.

We know that they regulate bowel movement by moderating intestinal peristalsis and they prevent overgrowth of toxicological bacteria by lowering intestinal pH. Studies have shown that toxin-producing Clostridium species can accumulate in the bowel when levels of Bifidobacteria have decreased.

Bifidobacteria synthesise the essential vitamins B1, B2, B6 and B12 which are necessary for a healthy nervous system and which are needed for the body to complete its digestive process. Moreover, they play a beneficial role in the synthesis of folic acid, niacin, pantothenic acid, and biotin.

This recent study simply adds to the growing body of knowledge supporting probiotics in many aspects of health.



* There are 20 times more bacteria in our guts than there are human cells in the body.

* There’s about 1kg of bacteria in our colons.

* We have more bacteria in our bodies than there have ever been people on the planet.

* Probiotic comes from the Greek words meaning “for life”.

*  The World Health Organisation defines probiotics as “live micro-organisms which, when administered in adequate amounts, confer a health benefit on the host”.


So what are the things to look for when choosing a probiotic supplement?

Most brands bank on the fact that many will go by therapeutic benefit (as judged by the specific strain used) and strength (number of CFUs), and develop their formulations accordingly. Then it’s up to you to test how well they actually work.

Quality probiotic supplements begin with well-considered formulations and quality manufacturing. Most importantly, you should choose a brand of probiotics that are backed by scientific research that puts their formulations to the test.

Emed makes it easy by doing the ground work for you!

Click here for Emed’s Best Probiotics.



Further Reading:



Shinji Fukuda, Hidehiro Toh, Koji Hase, Kenshiro Oshima, Yumiko Nakanishi, Kazutoshi Yoshimura, Toru Tobe, Julie M. Clarke, David L. Topping, Tohru Suzuki, Todd D. Taylor, Kikuji Itoh, Jun Kikuchi, Hidetoshi Morita, Masahira Hattori & Hiroshi Ohno, ‘Bifidobacteria can protect from enteropathogenic infection through production of acetate’, Nature 469, 543–547 (27 January 2011) doi:10.1038/nature09646