Nonpathogenic organisms are those that do not cause

disease A disease is a particular abnormal condition that negatively affects the structure or function of all or part of an organism, and that is not immediately due to any external injury. Diseases are often known to be medical conditions that a ...

, harm or death to another organism. The term is usually used to describe

bacteria Bacteria (; singular: bacterium) are ubiquitous, mostly free-living organisms often consisting of one Cell (biology), biological cell. They constitute a large domain (biology), domain of prokaryotic microorganisms. Typically a few micrometr ...

. It describes a property of a bacterium – its inability to cause disease. Most bacteria are nonpathogenic. It can describe the presence of non-disease causing bacteria that normally reside on the surface of

vertebrates Vertebrates () comprise all animal taxa within the subphylum Vertebrata () (chordates with backbones), including all mammals, birds, reptiles, amphibians, and fish. Vertebrates represent the overwhelming majority of the phylum Chordata, with c ...

and

invertebrates Invertebrates are a paraphyletic group of animals that neither possess nor develop a vertebral column (commonly known as a ''backbone'' or ''spine''), derived from the notochord. This is a grouping including all animals apart from the chordat ...

as commensals. Some nonpathogenic microorganisms are commensals on and inside the body of animals and are called microbiota. Some of these same nonpathogenic microorganisms have the potential to cause disease, or being pathogenic, if they enter the body, multiply and cause symptoms of

infection An infection is the invasion of tissues by pathogens, their multiplication, and the reaction of host tissues to the infectious agent and the toxins they produce. An infectious disease, also known as a transmissible disease or communicable dis ...

Immunocompromised Immunodeficiency, also known as immunocompromisation, is a state in which the immune system's ability to fight infectious diseases and cancer is compromised or entirely absent. Most cases are acquired ("secondary") due to extrinsic factors that a ...

individuals are especially vulnerable to bacteria that are typically nonpathogenic; because of a compromised

immune system The immune system is a network of biological processes that protects an organism from diseases. It detects and responds to a wide variety of pathogens, from viruses to parasitic worms, as well as cancer cells and objects such as wood splint ...

, disease occurs when these bacteria gain access to the body's interior. Genes have been identified that predispose disease and infection with nonpathogenic bacteria by a small number of persons. Nonpathogenic ''

Escherichia coli ''Escherichia coli'' (),Wells, J. C. (2000) Longman Pronunciation Dictionary. Harlow ngland Pearson Education Ltd. also known as ''E. coli'' (), is a Gram-negative, facultative anaerobic, rod-shaped, coliform bacterium of the genus '' Esc ...

'' strains normally found in the gastrointestinal tract have the ability to stimulate the immune response in humans, though further studies are needed to determine clinical applications. A particular strain of bacteria can be nonpathogenic in one species but pathogenic in another. One species of bacterium can have many different types or strains. One strain of a bacterium species can be nonpathogenic and another strain of the same species can be pathogenic.

References

{{portal bar, Biology Bacteriology Gram-positive bacteria Gram-negative bacteria Immune system