Yogurt may help combat colitis

Editor's note:  The following work comes out of Wendy Garrett's lab at Harvard.  Wendy will be an upcoming guest on the podcast.  If you have questions for her, feel free to email or call, and we will ask her on the show. 

A key signature of colitis is the build-up of reactive oxygen species (ROS) in the colon due to chronic inflammation.  One of major functions of ROS is actually to act as an antibiotic, and destroy any foreign bacteria that may exist at the site of inflammation.  However, ROS are known to be toxic to the host as well, and their high concentrations in colitis are likely a major contributor to the disease.  With this in mind, researchers at Harvard studied how probiotics from yogurt could ameliorate the disease by disposing the excess ROS.  They published their results last month in the Proceedings of the National Academy of Sciences.

The researchers had previously determined that a common yogurt that contained 5 strains of bacteria was helpful in decreasing symptoms in multiple mouse models of colitis.  In this study though, they identified Lactococcus lactis as being the most important of these strains in treating colitis symptoms.  They then compared the genome of L. lactis with the other strains in the yogurt and determined that a specific gene that codes for the enzyme, superoxide dismutase (SOD), which is capable of breaking down superoxide, an ROS, may be imparting L. lactis’ beneficial effects.  In order to support this hypothesis, the scientists showed that when this gene was removed from L. lactis the bacteria no longer reduced colitis.  They took this notion a step further and showed that superoxide levels were in fact decreased in vitro when combined with lysed L. lactis.  Finally, the scientists showed that the L. lactis must actually be lysed in the colons in order to release its SOD, destroy superoxide, and reduce colitis: when the scientists attempted to deliver SOD on its own to mice with colitis it was not as effective, and caused diarrhea.

This study is really interesting for two reasons.  The first is that it shows yogurt, like Activia, may be very helpful in dealing with colitis.  The second reason though, is that it shows a new system for deliverying SOD to a site of inflammation: via bacteria.  As they showed in the paper, simply using SOD was not effective, but using the bacteria as a vehicle for SOD, and then lysing it at the site was an effective means of drug delivery.  This has many important implications because ROS are important contributors to a variety of diseases.  

We've domesticated chickens and cows, how about probiotics?

Domesticated pig

Desended from wild boar

I recently came across an interesting article from Nature's Scientific Reports that discusses the ongoing domestication of bacteria by humans.  We are all well aware of domestication of animals and plants, but have we ever considered domesticating bacteria? One consequence in animals is that the domestic versions does not resemble their wild counterparts.  Striking examples are the large, white domestic ducks that are actually originally descended from the common mallard, or sheeps, which do not resemble the wild mouflon.  Another consequence is that the domesticated animals lose genetic diversity.  You may have heard stories about bananas which are at extreme risk for disease because of their monogenetic cultivation, or how many farm breeds across the world are going extinct putting the entire population of that animal at risk.  In the article researchers investigated how Lactobacillus acidophilus has changed since being used in dairy foods and probiotics.

 L. acidophilus is a unique bacteria because it can convert carbohydrates to lactic acid.  Humans then, harness the bacteria to create fermented foods like yogurt.  Because of its use in yogurt, and its general recognition as being safe by the FDA, many Lactobacillaea are used in probiotics, and we have written about the results of studies using them before.  The researchers in this study examined many different strains of L. acidophilus from all over the world and dating back to 1922 to see how the species has changed.  As it turns out, much like the domesticated plants and animals, all the strains tested had incredible genetic homology, with each strain being incredibly similar to the next.  The authors believe that this strain is very robust, and that it sits in a very advantageous place in evolutionary space, so that it is difficult for mutations to take hold.  This species can be thought of as an evolutionary bottleneck.  This may have given this strain an upper hand in being selected by early manufacturers, who did not want variation between batches and starter cultures.

 One may wonder though, does this put L. acidophilus at risk for disease?  As it turns out the bacteria appears to be very resistant to disease.  While it is attacked by many phages, these do not seem to affect the overall reliability of the species.  Again, this resiliency speaks to its use in manufacturing.  So the next time you are downing some delicious greek yogurt, remember that it likely tastes the same as when the ancient greeks were eating it too!