I keep pointing out to everyone how insanely complex is the human biome. Everything affects everything else in a tangle that is beyond convoluted. Well, just when you think you have something of a handle on that concept, some other piece of research comes out to show you just how wrong you are!
I’ve touched on this idea once or twice before on this blog: how a particular kind of bacteria are good except when they’re not. (As one example, check out this post on B. fragilis!) Yesterday though, reading about research just published out of the University of Vermont – published in the Proceedings of the National Academy of Science, no less – all I could think is, what we currently know about the biome is like looking at the proverbial tip of the iceberg.[i] How many times have I written about the health benefits of Lactobacillus reuteri?! It is great for you, right? Look, here in this post I talk about how it’s being used to treat PTSD and autism. And here, I talk about it how crucial it is for developing immune tolerance. L. reuteri is a normal, commensal bacteria and is very commonly used in probiotic mixes.
Except…these researchers found that it can actually increase the severity of multiple sclerosis (MS) in a mouse model. But only sometimes. Genetics matter. Great – yet another thing that will have to be taken into account as scientists work toward personalizing microbiome treatments. As the lead researcher on this study states, “Our gut bacteria are part of a complex ecosystem that holds great potential for the prevention, treatment, and/or diagnosis of chronic diseases. However, many scientists have been going at it with a one-size-fits-all approach, and our research suggests that this is unlikely to work…Instead, a more personalized approach is needed.”[ii] To sum up the findings of this work:
Researchers tested mice with a high and low genetic susceptibility to autoimmune encephalomyelitis (EAE) – 29 distinct genotypes. EAE is the most common animal model for MS. They isolated different bacterial species from the animals and transferred these to new mice, one at a time. L. reuteri was pinpointed as problematic in worsening MS symptoms in one particular genotype. However, the scientists noted that the L.reuteri was originating from the guts of the resistant-to-MS mice…which suggested to them that whether or not the bacteria was good or evil depended on the genetics of the mouse.
As though that’s not confusing enough, the researchers also point out that the strains of bacteria used in probiotic mixes are different from the ones naturally found in the intestinal biome. And worse yet, other scientists have used high doses of probiotics with a variety of Lactobacillus strains to REDUCE MS disease in mice. In fact, a study last year suggested that L. reuteri may be a novel treatment for MS! From that 2019 study, “In this study, we showed that probiotic Lactobacillus reuteri DSM 17938 (L. reuteri) ameliorated the development of murine experimental autoimmune encephalomyelitis (EAE), a widely used animal model of MS…”[iii]
Just when you think things can’t get more complicated, right? Never say never…
[iii] He, B, et. Al. Lactobacillus reuteri reduces the severity of experimental autoimmune encephalomyelitis in mice by modulating gut microbiota. Frontiers in Immunology. 2019;10(385). doi: 10.3389/fimmu.2019.00385