Gut bacterial flora is the complex community of microorganisms that live in the digestive tract of many animals and insects. In humans, the gut contains the greatest number of bacterial species and is established at one or two years of age. The relationship between an individual and their flora is an important symbiotic one, and changes in the specific make-up can have noticeable physiological effect on the human.
Some human gut microorganisms aid the host by fermenting dietary fibre into short-chain fatty acids (SCFAs), while others play a role in metabolising bile acids, sterols and xenobiotics and synthesising vitamin B and vitamin K. The biological importance of these compounds is similar to that of hormones, and, therefore, dysregulation of the gut flora has been correlated with a number of inflammatory and autoimmune conditions.
Moreover, for the past few years, it has also been known that gut bacteria can have an effect on our emotions. In fact, some species produce the same molecules as those that are used in brain signalling, such as dopamine, serotonin and gamma-aminobutyric acid (GABA). Since the brain is predominantly made up of fats, the SCFAs produced by the metabolic activity of bacteria also influence neural health.
Research conducted in 2011 by a team at North Carolina State University showed that a type of gut bacteria, called Lactobacillus rhamnosus, can dramatically alter GABA activity in the brains of mice, as well as influencing how they respond to stress. Their work illustrated that chronic treatment with L. rhamnosus “reduced stress-induced corticosterone and anxiety- and depression-related behaviour”.
Recently, work done by Philip Strandwitz and his team at Northeastern University in Boston has brought a new gut bacteria, KLE1738, to light. They discovered that this strain would only grow in the presence of GABA. Since GABA acts by inhibiting signals from nerve cells and low levels are linked to depression and mood disorders, this discovery further supports the hypothesis that gut flora affects brain function.
It has been suggested that further research into the link between gut microorganisms and neural molecules may eventually lead to new and personalised treatments for disorders such as depression and anxiety. While a search for a “cure” may be somewhat far-fetched, improved understanding may have a significant on improving patients’ quality of living.