Microbial infection is the combinatorial process of invasion of infectious agents into the organism, their multiplication and the reaction of host tissue against these agents. Infectious agents mainly include bacteria, virus, parasite, fungi etc.Different terms are used to describe infections. The first is an acute infection. An acute infection is one in which symptoms develop rapidly; its course can either be rapid or protracted. The next is a chronic infection. A chronic infection is when symptoms develop gradually, over weeks or months, and are slow to resolve. A sub acute infection is one in which symptoms take longer to develop than in an acute infection but arise more quickly than a chronic infection. A latent infection is a type of infection that may occur after an acute episode; the organism is present but symptoms are not; after time the disease can reappear. A focal infection is defined as the initial site of infection from which organisms travel via the bloodstream to another area of the body.