Scientists uncover how probiotics benefit health – research in Nature

From our colleagues at the AusSMC:

Research from Tokyo and Australia has provided the first-ever clues on the mechanisms underlying the beneficial effects of probiotics (bacteria that promote health).

Bifidobacteria, one of the most numerous such bacteria, confer to their hosts a range of beneficial health effects, aiding in digestion, boosting the immune system and even potentially reducing cancer risk. The mechanism underlying these effects, however, has remained a mystery until now.

Below, the study’s Australian Co-author and several Japanese scientists comment on the work.

Note: This roundup was done in collaboration with the Science Media Centre of Japan (SMCJ) with support from the Australia-Japan Foundation. Comments from Japanese scientists have been translated into English by the SMCJ. We welcome your feedback on this effort.


Dr David Topping is a Chief Research Scientist with CSIRO Food Futures and Preventative Health Flagships, based in Adelaide. He is a co-author on the Nature paper.

“There is a rapidly growing understanding that the gut bacteria (long thought to be bad) are extremely beneficial for health. These beneficial bacteria (probiotics) exert a wide range of effects through the products of their metabolism of dietary fibre carbohydrates. These products are called short chain fatty acids (SCFA) and this study has looked at how one of these acids, acetic acid, could confer protection against a highly pathogenic organism E coli 0157. This bacterium poses a major threat of food-borne infection. While protection was shown with probiotic Bifidobacteria, the study showed also that a CSIRO technology being developed in Preventative Health Flagship was also highly effective. This product is a modified starch which delivers specific SCFA to the large bowel and the data confirm that acetic acid was critical for survival of infected animals. The studies offer promise for the development of more effective prebiotic and probiotic foods to assist in infection control.

The project is extremely exciting both in terms of basic research and also its application. CSIRO have been collaborating with Japanese scientists in this area for some years now, but it is the first time we have worked with the RIKEN group. The success of the project opens up a whole range of new opportunities for joint work.”

Associate Professor Eiichi Sato, Microbiology Lab., Dept. of Applied Biology and Chemistry, Tokyo University of Agriculture

“Bifidobacteria, along with lactic acid bacteria, are a strain of probiotics with promising health effects. It is, however, microbiologically different from lactic acid bacteria because in addition to producing lactic acid, it also produces a large amount of acetic and formic acid. This research shows that the acetic acid produced from a bacteria strain within bifidobacteria becomes a defence against enterohaemorrhagic Escherichia coli O157:H7 infections.

There have been a number of studies showing that metabolites produced by probiotics are linked to preventing infectious diseases. But this latest study is a breakthrough because it has used the latest technology, such as metagenomics and omics analysis, to see how the defence mechanism works precisely. On the other hand, it must be stressed that these experiments were carried out using germ-free mice and cultured cells. Of course, it’s normal for germ-free mice and cultured cells to be used in these sorts of tests and I wouldn’t be exaggerating when I say that it would’ve been impossible to run analyses without them.

However, thinking about it in terms of 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. Therefore, it would be difficult to apply this experiment the way it is exactly onto humans since these results were gathered using cultured cells and germ-free mice. This is a dilemma many scientists struggle with. But bifidobacteria are a well-known strain of probiotics so I think it would be safe to expect that some day someone will be able to clarify our defence mechanism against diseases.”

Professor Atsushi Yokota, Microbial Physiology Lab., Research Faculty of Agriculture, Hokkaido University

“Using the most up to date techniques and experiments using mice, Dr Fukuda and his team were able to find that bifidobacteria enterohemorrhagic Escherichia coli O157:H7 could protect the mice from dying of infectious diseases. Over the last few years, scientists have found that lactic acid bacteria and bifidobacteria have health-promoting effects, but how they did exactly had never been fully understood.”

What this study found was that the acetic acid produced inside the large intestine by bifidobacteria and fermenting fructose plays an important role. It is well-known that colonic epithelial cells (cells on the surface) grow a number of organic acids, including acetic acid, as an energy source. This paper shows that strong strains of bifidobacteria help fermenting fructose keep the acetic acid inside the colon healthy, allowing more of it to be made. This effectively stops Shiga toxins made by O157 inside the intestine from moving into the blood stream and helps the mouse to survive.

In contrast, strains of bifidobacteria that were not able to protect mice from dying of infectious diseases had failed because it wasn’t able to bring in enough fructose inside its cell, resulting in not enough acetic acid being produced. In addition to this, introducing a strain of bifidobacteria where the mechanism to bring fructose into the cell had been broken resulted in significantly smaller amounts of acetic acid being produced, and therefore the protection against O157 infections had been lost.

In the past, it had been known that acetic acid made from carbohydrates fermented by bifidobacteria had health benefits, but this is the first time anyone had clearly proved it.Intestines already contain organic acids such as acetic acid because of the bacteria already there. This paper has helped demonstrate how important these bifidobacteria strains are in maintaining our health, and what is needed to keep them healthy.

However, the study does not say that it is a good idea to drink vinegar in order to increase the body’s acetic acid concentration. What’s important is to keep bifidobacteria and other intestinal bacterial flora healthy. In order to do this it is important to follow a balanced diet with plenty of fibre and oligosaccharides. You could say that today’s report tells us how bacteria in our intestines protect our health, and how important it is to follow a balanced diet.”