We Are Our Germs

This sort of thing sets me thinking:

For the first time, researchers at McMaster University have conclusive evidence that bacteria residing in the gut influence brain chemistry and behaviour.

The findings are important because several common types of gastrointestinal disease, including irritable bowel syndrome, are frequently associated with anxiety or depression. In addition there has been speculation that some psychiatric disorders, such as late onset autism, may be associated with an abnormal bacterial content in the gut. "The exciting results provide stimulus for further investigating a microbial component to the causation of behavioural illnesses," said Stephen Collins . . . .

For each person, the gut is home to about 1,000 trillion bacteria with which we live in harmony. These bacteria perform a number of functions vital to health: They harvest energy from the diet, protect against infections and provide nutrition to cells in the gut. Any disruption can result in life-threatening conditions, such as antibiotic-induced colitis from infection with the "superbug" Clostridium difficile.

Working with healthy adult mice, the researchers showed that disrupting the normal bacterial content of the gut with antibiotics produced changes in behaviour; the mice became less cautious or anxious. This change was accompanied by an increase in brain derived neurotrophic factor (BDNF), which has been linked, to depression and anxiety.

When oral antibiotics were discontinued, bacteria in the gut returned to normal. "This was accompanied by restoration of normal behaviour and brain chemistry," Collins said.

What if part of our personality is determined by the bacteria that live inside us? What if different bacteria would change who we are? What if there are differences between the bacteria that inhabit different human communities, causing certain groups of people to be, on average, more or less anxious, or more or less energetic? What if different diets change our bacteria, and therefore our personalities?