Final answer:
An infection is the successful colonization of a host by a microorganism. It can be categorized as local, focal, or systemic depending on its spread in the body.
Step-by-step explanation:
An infection is a successful colonization of a host by a microorganism. It can be classified as local, focal, or systemic depending on the extent to which the pathogen spreads in the body. In a focal infection, a localized pathogen or the toxins it produces can spread to a secondary location. For example, a dental hygienist nicking the gum with a sharp tool can lead to a local infection in the gum by Streptococcus bacteria of the normal oral microbiota, which may then spread to other locations in the body.