The term infection refers to microorganisms colonizing the body. contact with microorganisms. contact with pathogens. pathogens penetrating host defenses.

Infection is a general term referred to the invasion of foreign microorganisms into our body. These foreign microorganisms include bacteria, viruses, parasites and pathogens. They should come from outside the body to be considered as an infection. Symptoms may or may not effect from it. 

The answer is microorganisms colonizing the body.