A reader messaged me:
There reports of people improving using VNS recently; came across this.
https://bioelecmed.biomedcentral.com/articles/10.1186/s42234-018-0004-9A reader via facebook
How could this affect the good vs bad bacteria in one’s microbiome?
We have recently reported in a 6 month follow-up pilot study that VNS improves active Crohn’s disease. Preliminary data of another pilot study confirm this interest. Similarly, VNS has recently been reported to improve rheumatoid arthritis, another TNFα mediated diseaseIs-there a place for vagus nerve stimulation in inflammatory bowel diseases? 
- Towards improved control of inflammatory bowel disease  “. Clinical studies using implanted vagus nerve stimulators for treatment of IBD show encouraging results. “
As a starting point, let us look at how the mind impacts the microbiome due to stress. We see a relatively long list of bacteria associated with stress reported on the national library of medicine. The state of the mind impacts the microbiome; also the microbiome impacts the state of mind (depression, sleeplessness etc). Some readings:
- The Microbiome-Gut-Brain Axis and Resilience to Developing Anxiety or Depression under Stress 
” Stress alters the gut microbiota and plausibly this could contribute to stress-related changes in mood”
The study above is also cited in
- Alzheimer’s disease: An evolving understanding of noradrenergic involvement and the promising future of electroceutical therapies  Alzheimer’s disease also has distinctive microbiome shifts.
- Non-invasive vagus nerve stimulation improves clinical and molecular biomarkers of Parkinson’s disease in patients with freezing of gait  Which also has microbiome shifts.
Back to a mechanical/chemical approach to the analysis. What do we know change with vagus nerve stimulation. Remember, a change of circulating chemicals will influence bacteria growth.
- releases glucocorticoids
- release of acetylcholine 
- anti-inflammatory cytokine interleukin-10 (IL-10) Specific vagus nerve stimulation parameters alter serum cytokine levels in the absence of inflammation 
- serum TNF Parameters matter: modulating cytokines using nerve stimulation 
The central nervous system recognizes peripheral inflammation via afferent vagus nerve signaling. The brain can attenuate peripheral innate immune responses, including pro-inflammatory cytokine production, leukocyte recruitment, and nuclear factor kappa β activation via α7-nicotinic acetylcholine receptor subunit-dependent, T-lymphocyte-dependent, vagus nerve signaling to spleen.The vagus nerve and the inflammatory reflex: wandering on a new treatment paradigm for systemic inflammation and sepsis 
Vagus nerve stimulation alters the chemicals in the body. Studies in mice with electronic stimulation indicate that it can make inflammation worse or better — depending on the parameters. There are a wide variety of methods to stimulate the vagus nerve — a few common ones[src] are:
- Cold Exposure. …
- Deep and Slow Breathing. …
- Singing, Humming, Chanting and Gargling. …
- Probiotics. …
- Meditation. …
- Omega-3 Fatty Acids.
- Exercise. …
The use of electronic means should be done with caution because the setting used can have an adverse effect (according to mice studies). This may also apply to exercise with ME/CFS.
While I could not find studies explicate for CFS/ME, I did find some for items often co-mobid with ME/CFS
- The Effects of Noninvasive Vagus Nerve Stimulation on Fatigue and Immune Responses in Patients With Primary Sjögren’s Syndrome  “production of IL-6, IL-1β, IP-10, MIP-1α, and TNFα were significantly reduced over the study period. Patterns of NK- and T-cell subsets also altered significantly over the study period.”
- Chronic fatigue syndrome from vagus nerve infection: a psychoneuroimmunological hypothesis 
I have concern over arbitrary vagus stimulation with ME/CFS, especially electronic means. I know too many people that have adverse reaction to exercise, humming, singing etc. In some of these cases, it is possible that the adverse reaction may be connected to a vagus nerve infection.