Lactose: Food for Gut Infection/Dysbiosis?

This little article caught my attention.[i]  It’s an animal study so it may not be applicable to humans…but it’s certainly something on which I should keep an eye.  As you all know, I’m especially interested in the connection between food and gut bacteria.

A particular kind of bacteria, Enterococcus, are “particularly risky” for people who are immune compromised – for example, those having bone marrow transplants or those on immune suppressors following an organ transplant.  It can cause a serious infection.  It turns out that (at least in mice), lactose, the kind of sugar found in milk and dairy products, feeds Enterococcus.

In a study of 1,300 people with bone marrow transplants a definitive link was found between Enterococcus and a potentially lethal immune condition called graft-versus-host disease (wherein immune cells attack the newly transplanted organ).

After giving mice bone marrow transplants, their intestines could no longer produce lactase, the enzyme that breaks down lactose for digestion:  “The high levels of undigested lactose in turn led to a total domination of Enterococcus.”  (The theory is that the chemotherapy agents given to those getting a bone marrow transplant damages the cells which line the intestines, the enterocytes. These cells produce the enzymes which break down disaccharide sugars like lactose.)

The researchers were shocked at these results.  What’s even crazier is that when the scientists cultured this bacteria in vitro, and added lactase (in the form of the over-the-counter pill, Lactaid), growth of Enterococcus was blocked.  They, therefore, started to feed it to their lab mice and low-and-behold, the mice were protected from Enterococcus growth.

While not as yet tested in humans, there is existing data that suggests the same connection.  People with the gene that tends to make them more lactose-intolerant are already known to have a harder time clearing Enterococcus from their gut biome.  The researchers are contemplating a trial in humans who are on chemotherapy drugs to test the efficacy of Lactaid and/or the removal of lactose from the diet.

I took a quick look around to see what other illnesses with which Enterococcus might be associated.  According to the Merck Manual, two strains of Enterococcus (Enterococcus faecalis and E. faecium), “…cause a variety of infections, including endocarditis, urinary tract infections, prostatitis, intra-abdominal infection, cellulitis, and wound infection as well as concurrent bacteremia.”[ii]  (Bacteremia means bacteria in the blood…which is a really, really bad thing (like sepsis).)  Perhaps even more interesting:  studies in people with Crohn’s have shown greatly increased levels of Enterococcus as compared to healthy controls.[iii]  According to this paper, this species is associated with intestinal inflammation, at least in animal models.

I don’t yet know what to make of all this.  It struck me, reading all this, that the Specific Carbohydrate Diet – which for so many years has proven unbelievably successful for treating inflammatory bowel diseases – requires the complete removal of disaccharides like lactose from the diet.  Coincidence?

I think  it’s worth following this research in the future, right?

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[i] https://www.mskcc.org/blog/milking-it-study-mice-suggests-lactose-diet-feeds-dangerous-gut-bacteria?_subsite=research-ski

[ii] https://www.merckmanuals.com/professional/infectious-diseases/gram-positive-cocci/enterococcal-infections

[iii] Yu, L.C. Microbiota dysbiosis and barrier dysfunction in inflammatory bowel disease and colorectal cancers: exploring a common ground hypothesis. J Biomed Sci 25, 79 (2018) doi:10.1186/s12929-018-0483-8