What causes stomach bacteria?

Just as organisms have evolved to survive in a rock pool or under the bark of a tree, so to has bacteria evolved to survive in the stomach of humans and animals. One pound of the weight of an adult human is from bacteria alone. These bacteria are largely beneficial and prevent pathogenic (illness inducing) bacteria such as pathogenic E. Coli from multiplying by competing for space and nutrients. As to what causes it, when a newborn is breastfed the milk contains enzymes and bacteria (without exposing the baby to these it will have a weaker immune system as an infant). Bacteria grow from this milk and continue to grow until the body cools after death. Food introduces new bacteria (even if it looks Exceedingly Good) which is usually out competed and dies, or it may cause illness (such as food poisoning or stomach upset) and be flushed out by time or drugs. Post by James Johnson