Volume 7 Issue 5 May, 2017
Consultation Liaison Psychiatry Focus: Microbiology
Much before the advent of modern medicine and systematic studies in mental health and neurosciences, diet has been
hypothesized to be an important factor in maintaining mental health. Special mention to be made here is Ancient Indian Medicine – Ayurveda laid special emphasis on diet. There had been various theories in west during late 18th & 19th and even early 20th centuries about colonic auto intoxication leading to infections causing neuroses which were later termed absurd and quackery because they advocated radical methods like colonic purging and bowel resection etc. It is only recently that there is a spurt in research interest exploring links with microbiome of gut that may influence central nervous system right from the growth and maintenance. We know that our body contains 10 times more microbial cells than our own body cells. Microbiome in the gut is estimated to be 100 trillion with more than 1000 species. Many recent studies in the reputed journals have shown the inseparable relation between gut microbiome and brain development and function. For example, germ free mice have autistic like behavior, which were treated with addition of regular microbiome. There are studies linking dysbiosis in the gut flora to Alzheimer’s. In another study, Bifidobacterium longum administration caused reduction in the cumulative output of the stress hormone cortisol. Microbiome acts through various mechanisms.
- Activating Vagus nerve
- Activating the immune system – T regulatory cells
- Stimulating gut endocrine cells to release various factors or neurotransmitters such as
1. BDNF (Brain derived neurotrophic factor)
2. GABA – acts as distressing agent
3. Glutamate – helps in memory and cognitive function
4. Serotonin
- Metabolites released by microbes
There are two main enterotypes (ecosystems) known in the entire human population.
- Bacteroides and Ruminococcus type (enterotype 1)
- Prevotella type (enterotype 2)
Enterotype 2 is known to be healthy one and enterotype 1 is unhealthy. There are many reasons. Enterotype 2 produces many short chain fatty acids like acetate, propionate and butyrate, which suppress neuroinflammation. Enterotype 1 produces arachidonic acid (omega 6 fatty acid) metabolites, secondary bile acids and hydrogen sulfide, which promote inflammation. In another study, predominance of enterotype 2 was seen in native Africans and enterotype 1 was seen in African Americans with Western diet. Hence, the right diet supports the healthy enterotype (predominant Prevotella). Mainly plant based diet is known to produce this enterotype (Prevotella type). In a study published in Journal of Affective disorders (2014), omega 6 fatty acids are associated with greater risk of suicide and major depression in early pregnancy.
At this stage, the early evidences are firmly suggesting the inseparable link between gut and CNS and gut microbiome can be a potential area for intervention especially in preventive and positive mental health. It was advocated centuries before and now it has to be re-explored in the light of modern research.
Dr. Sumantha A, Assistant Professor, Dept. of Microbiology, Basaveshwara Medical College & Research Centre, Chitradurga drasumant@gmail.com
