(redirected from Commensal bacteria)
Also found in: Dictionary, Thesaurus, Medical.


commensalism (kəmĕnˈsəlĭzˌəm), relationship between members of two different species of organisms in which one individual is usually only slightly benefited, while the other member is not affected at all by the relationship. For example, some flatworms live attached to the gills of the horseshoe crab, obtaining bits of food from the crab's meals; the crab is apparently unaffected. In many cases commensalism cannot be distinguished from parasitism (see parasite). See also competition; symbiosis.
The Columbia Electronic Encyclopedia™ Copyright © 2022, Columbia University Press. Licensed from Columbia University Press. All rights reserved.
The following article is from The Great Soviet Encyclopedia (1979). It might be outdated or ideologically biased.



inquilinism, the cohabitation of animals of different species, whereby one (the commensal) benefits permanently or temporarily from the other without causing the latter any damage.

A commensal may use the other organism for protection or transportation, or it may take advantage of the latter’s food supply. Characteristically commensal animals are divided into three groups, according to the character of the interrelationship:

(1) The commensal limits itself to the use of the food of the organism of the other species; for example, the annelid Nereis lives in the coils of the shell occupied by the hermit crab and eats the crab’s leftover food.

(2) The commensal attaches itself, temporarily or permanently, to the body of the other species, in this case called the host; for example, the remora attaches itself by the dorsal fin, which has developed into a sucker, to sharks and other large fishes and uses them for transportation; certain marine hydroids settle on the skin of fish and feed on their excrement; and certain crustaceans (such as acorn barnacles) live on the skin of whales and the shells of mollusks.

(3) The commensal settles in the viscera of the host; for example, the infusorians of subclass Protociliata live in the rectum of frogs, and certain flagellates live in the intestines of mammals.

Parasitism may have originated evolutionarily from commensalism in which the commensal settles in the organs of the host. Symbiosis may also have been an elaboration of commensalism. However, commensalism is not an obligatory transitional step to parasitism or symbiosis; these forms of interrelationship may have originated independently of commensalism in the historical development of the given organisms.

The Great Soviet Encyclopedia, 3rd Edition (1970-1979). © 2010 The Gale Group, Inc. All rights reserved.


An interspecific, symbiotic relationship in which two different species are associated, wherein one is benefited and the other neither benefited nor harmed.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.
References in periodicals archive ?
Commensal bacteria play an essential role in protecting against infections, shaping and regulating immune responses, and maintaining host immune homeostasis.
In steady state, the gut is a rich source of TLR ligands from commensal bacteria, some of which have been recently associated with diseases in mouse models of colitis and in human inflammatory bowel diseases.
Germ-free mice, which are reared in a sterile environment and thus lack all live commensal bacteria, also showed similar responses to those observed in antibiotic-treated mice when exposed to HDM.
Interactions between commensal bacteria and gut sensorimotor function in health and disease.
Alenghat et al., "Innate lymphoid cells promote anatomical containment of lymphoid-resident commensal bacteria," Science, vol.
Studies in germ-free mono-contaminated experimental animals indicate that commensal bacteria may be involved in the pathogenesis of colonic inflammation (2).
In fact, high resistance rates have often been reported in surveillance studies dealing with clinical isolates (1,4,5) and in prevalence studies of commensal bacteria taken as indicators to estimate spread of acquired resistance (6-15).
Helminths (parasitic worms that have evolved to live in the intestines or other locations of their animal hosts) can cause disease; but, like commensal bacteria, they may also provide health benefits.
Moreover, a majority of commensal bacteria are Gram-positive and thereby have a high capacity for activation of TLR2 [6, 7].
Commensal bacteria, expressing unique enzymes, contribute to the digestion of dietary substances as well as the synthesis of food supplements [1].
Washington, June 18 ( ANI ): Researchers have identified commensal bacteria in the human intestine that produce a neurotransmitter that may play a role in preventing or treating inflammatory bowel diseases such as Crohn's disease.
Her research interests are marine mammals as indicators of fecal bacterial contamination in the marine environment, including pathogenic bacteria and antimicrobial drug-resistant commensal bacteria such as Escherichia coli.