Gut bacteria: The surprising impact of viruses

The microbiome plays a vital role in health. A recent study has investigated how viruses that kill gut bacteria influence these microbes. The findings make an already complicated picture much more so. The microbiome is both fascinating and fashionable.
The increase in public interest has provided a boost in funding to study the interactions between us and our gut bacteria. Scientists have now found relationships between the microbiome and a range of conditions, from diabetes and obesity to Parkinson's and depression.

Thanks to gut bacteria's high profile, grocery stores shelves are now brimming with probiotic products. Despite their wide availability and popularity, however, there is little evidence to suggest that they provide many benefits outside a small number of specific conditions. Although scientists know that the microbes within us are vital, designing a way to moderate them to improve health and fight disease is still a long way off.

The primary reason for this is the dazzling complexity of the microbiome. It is not a single, homogenous entity, but a world of microscopic beings that interact, influence, and inhibit their neighbors, capable of killing, nourishing, and communicating with each other. Already, at this point, we can see the vast difficulties in understanding the ins and outs of the microbiome, but some researchers are examining the next level of complexity: bacteriophages.



Bacteriophages, or simply phages, are viruses that exclusively destroy bacteria. Incredibly, phages outnumber bacteria; where there are bacteria, there are phages in spades.
Phages are specific, too; they tend to destroy just one species or strain of bacteria. Before the advent of antibiotics, scientists used phages to fight infections. However, when researchers discovered antibiotics, they took the place of phages; antibiotics were cheaper and easier to produce than phages. Now, with antibiotic resistance on the rise, some researchers are revisiting the idea of phage therapy.

Of course, if phages kill bacteria, they are likely to influence the microbiome. Researchers from the Brigham and Women's Hospital and the Wyss Institute, both in Boston, MA, are interested in exactly how these abundant viruses might impact our gut bacteria. They published the results of their most recent study in the journal Cell Host & Microbe.

To investigate, the researchers used gnotobiotic mice; they reared these animals in such a way that they have no bacteria living on or in them. To begin, they introduced to the mice 10 species of bacteria that commonly reside in the human gut, including Enterococcus faecalis and Escherichia coli.
Then, they added phages that specifically target the bacteria they transplanted into the mice. For instance, the T4 phage targets E. coli, and the VD13 phage attacks E. faecalis. They then tracked the success of each microbe.

The scientists showed that although any given phage attacked only one species of bacteria, that phage would also impact other species; some species thrived while others dwindled.
Looking at the wider picture, the researchers also assessed the array of compounds produced by both the bacteria and the mouse; this is called the metabolome.

They found that when they introduced a phage to the mice and the bacterial composition changed, there were also changes in the levels of certain biologically active chemicals. The study authors write: In other words, a single strain of a virus can alter the type or quantity of biological molecules available to the host animal.

My Take:
As I have repeatedly warned, your microbiome is unique. We just don’t know what probiotics live in your microbiome, so taking any probiotic is not without risk of damaging the microbiome or even triggering an autoimmune response.

Phage therapy holds a lot of promise and hopefully fills the void created by abuse of antibiotics over the past 50 years. I was not aware that phage therapy had been studied prior to the introduction of antibiotics during WWII.

Bottom Line:
Do everything you can to preserve and support your microbiome – eat fermented foods, take a prebiotic, increase the fiber in your diet. However, avoid probiotic supplementation unless a specific condition calls for short term use.

Source: June 19, 2019 NIH