All humans have enormous numbers of bacteria and other micro-organisms (10 to 14) in the lower intestine.
In fact our bodies contain about ten times more bacteria than our own cells and these tiny passengers are extremely important for our health. They help us digest our food and provide us with energy and vitamins.
These "friendly" commensal bacteria in the intestine help to stop the "bad guys" such as Salmonella that cause infections, taking hold. Even the biochemical reactions that build up and maintain our bodies come from our intestinal bacteria as well as our own cells.