Gut microflora is well-known to be involved in almost every digestive complaint: IBS, constipation, diarrhoea, post-antibiotic problems and so on. More recently, many scientific studies have appeared linking gut bacteria to behaviour such autism, anxiety and depressive illnesses.
We all have approximately 4 lbs of bacteria in our gastrointestinal system or gut. Each and every one of us has their own individual profile of gut microflora. This microflora is picked up in the birth canal during childbirth. (Caesarian births experience a different implantation). A baby also gets a small amount of microflora through breast milk and also a little from skin contact - from Dad!
There are 'good' guys and 'bad' guys so it is a question of keeping these bacteria balanced. All the 'bad' guys can not be eradicated and they also have their uses. It is estimated there are over a billion different species of bacteria in our digestive system making more bacteria than cells in our bodies.