infection - Colonization

The invasion of the body by micro-organisms that are capable of multiplying there and producing illness. Such organisms are called pathogenic. However, some pathogenic organisms can exist on the skin or in other parts of the body without causing illness; in these circumstances the individual is said to be a ‘carrier’ of the organism. An infection begins by the entry of an organism at a specific site, such as the tonsils, skin, urinary, and respiratory tracts. This is followed by a short interval in which the person feels well (the incubation period), during which the micro-organisms multiply. They may cause disease locally or disperse throughout the body causing disease in other tissues and organs, such as in cystitis (the bladder), pneumonia (the lungs), and hepatitis (the liver).

An infection is the detrimental colonization of a host organism by a foreign species. In infection, the infecting organism seeks to utilize the host's resources in order to multiply (usually at the expense of the host). The infecting organism, or pathogen, interferes with the normal functioning of the host and can lead to chronic wounds, gangrene, loss of an infected limb, and even death.

Colonization

Wound colonization refers to nonreplicating microorganisms within the wound, while in infected wounds replicating organisms exist and tissue is injured. All multicellular organisms are colonized to some degree by extrinsic organisms, and the vast majority of these exist in either a mutualistic or commensal relationship with the host. Organisms which are normally non-pathogenic can become pathogenic under the right conditions, and even the most virulent organism requires certain circumstances to cause a compromising infection. Some colonizing bacteria, such as Corynebacteria sp. and viridans streptococci, prevent the adhesion and colonization of pathogenic bacteria and thus have a symbiotic relationship with the host, preventing infection and speeding wound healing.

The variables involved in the outcome of a host becoming inoculated by a pathogen and the ultimate outcome include:

the route of entry of the pathogen and the access to host regions that it gains the intrinsic virulence of the particular organism the quantity or load of the initial inoculant the immune status of the host being colonized

As an example, the staphylococcus species present on skin remain harmless on the skin, but, when present in a normally sterile space, such as in the capsule of a joint or the peritoneum, will multiply without resistance and create a huge burden on the host.