The liver is, like the intestine, a very hostile environment. However, in addition to defending itself against digestive juices, there are two other problems.

The first is immune response. The liver is an internal organ, where many immune responses originate. The liver helps the body resist infection by producing immune factors and by removing bacteria from the bloodstream.

The second problem is its location. The liver is not a part of the digestive system, and thus is not passed through on the direct path when someone eats something. Thus in order to survive in the liver, an organism must be able to easily move of its own accord through the body.