Student - February 12, 2009


Microbiologist Dr. Michiel Kleerebezem has shown for the first time that a probiotic bacteria of the type put into commercial drinks has an observable effect on the human immune system. His article appeared in Proceedings of the National Academy of Sciences (PNAS).

‘It has already been shown that probiotics can have a positive effect on people with bowel problems’, says Kleerebezem. ‘But it is harder to prove that someone with no particular problems becomes even healthier. Our research proved that the lining of the intestines of healthy people showed a reaction that can contribute to improved protection against pathogens.’

During this study, eight healthy, non-smoking adults were given an energy drink with or without the bacteria lactobacillus planetarium. A few hours later, samples were taken from the upper small intestine. Kleerebezem: ‘We tested the samples for the molecular reaction in the intestinal epithelium, to see how that part of the intestine reacts to the bacteria. It appears that the immune system is activated, without any big anti-infection responses going on. The intestinal cells are put on red alert so that they could respond quickly to disease carriers. Whether that actually happens is something we haven’t investigated.’

In spite of the small number of subjects, Kleerbezem was able to draw clear conclusions. ‘We have looked at thousands of genes and have concentrated on characteristics that were specifically stimulated in all eight subjects. People vary tremendously, and there is a lot of variety in gene activity too. But we still found a clear reaction.

Another striking result was that it also makes a difference which growth stage the bacteria is in. Bacteria that were added to the drink during the logarithmic phase had much less effect on the immune system than bacteria that were fully grown.

Kleerebezem: ‘You can conclude from our study that it makes a difference not only which sort of bacteria you use, but also how the bacteria is produced and how the drink is made. It is not just the number of living cells that matters, but also the basis of the drink. A milk product can give a different effect that a fruit juice.’

A question that remains after this research is which molecules of the bacteria are important for the immune responses. The research question then shifts toward the molecular communication mechanism that is at work between bacteria and human cells. Kleerebezem: ‘If we can get a better picture of the reaction mechanisms, then claims made by producers of these sorts of drinks can be supported better, and can be verified. That is not yet possible with this study, as we used a model organism that isn’t in commercial drinks. So it has not been proved that all probiotics have the same effect.