Re: How does the bacterium E.coli get into the intestional system ??

The first question that needs to be addressed is how do bacteria get to the 
intestine in the first place. The major route of colonizing the intestine 
is through the mouth. It has been shown in studies in mice that the 
intestine is colonized within the first few days of life, and that within a 
few weeks the bacteria have reached levels that are seen in the adult 
mice.Although it is possible to colonize the intestine through the anus 
this is a very minor means of entry into the host, and may generally be 
ignored.

If the major route of colonizing the intestine is through the mouth how do 
they get through the stomach? The stomach is an acidic environment and is 
full of digestive enzymes. This means that bacteria which are sensitive to 
the acidic environment and digestion are efficiently killed. But if a 
bacteria is resistant to the acidic environment and digestive enzymes it is 
not eficiently killed. When considering the passage of bacteria through the 
stomach one must remember that there is as much diversity in a single 
species of bacteria, such as E. coli, as there is in the entire human 
population, which is only a single species. In fact there are more E. coli 
in your intestine than there are people on the earth. This means that 
although E.coli is generally acid sensitive, and thus killed by the 
stomach, there is always a small percentage of E. coli that is acid 
resistant and thus survives passaage through the stomach.