Colonization resistance is the mechanism whereby the

intestinal microbiota Gut microbiota, gut microbiome, or gut flora, are the microorganisms, including bacteria, archaea, fungi, and viruses that live in the digestive tracts of animals. The gastrointestinal metagenome is the aggregate of all the genomes of the gut mi ...

protects itself against incursion by new and often harmful microorganisms. Colonization resistance was first identified in 1967, and it was initially referred to as antibiotic associated susceptibility. It was observed that animals being treated with the antibiotic

streptomycin Streptomycin is an antibiotic medication used to treat a number of bacterial infections, including tuberculosis, ''Mycobacterium avium'' complex, endocarditis, brucellosis, ''Burkholderia'' infection, plague, tularemia, and rat bite fever. F ...

were susceptible to ''

Salmonella enterica ''Salmonella enterica'' (formerly ''Salmonella choleraesuis'') is a rod-headed, flagellate, facultative anaerobic, Gram-negative bacterium and a species of the genus ''Salmonella''. A number of its serovars are serious human pathogens. Epidemi ...

'' at doses 10,000 fold lower than the standard minimal infectious dose. This led to investigations about the mechanisms utilized by endogenous microbial populations that conferred protection against exogenous pathogens attempting to colonize the gut flora. It has been observed that colonization resistance can occur within the host in a 'direct' or 'indirect' manner. The former refers to particular components of the microbiota directly competing with exogenous pathogens for nutritional niches (e.g. ''E. coli'' directly competes with ''

Citrobacter rodentium ''Citrobacter rodentium'' is a Gram-negative species of bacteria Bacteria (; singular: bacterium) are ubiquitous, mostly free-living organisms often consisting of one biological cell. They constitute a large domain of prokaryotic micr ...

'' for carbohydrates in the

intestinal lumen The gastrointestinal tract (GI tract, digestive tract, alimentary canal) is the tract or passageway of the digestive system that leads from the mouth to the anus. The GI tract contains all the major organs of the digestive system, in humans and ...

) or by producing growth inhibitors (e.g. ''Bacteroides thuringiensis'' can secrete

bacteriocin Bacteriocins are proteinaceous or peptidic toxins produced by bacteria to inhibit the growth of similar or closely related bacterial strain(s). They are similar to yeast and paramecium killing factors, and are structurally, functionally, and ec ...

that directly targets spore-forming '' Clostridium difficile'', thus inhibiting its growth through an unknown mechanism), that directly inhibits the colonizing pathogen. Indirect colonization resistance is thought to be mediated through the induction of

immune In biology, immunity is the capability of multicellular organisms to resist harmful microorganisms. Immunity involves both specific and nonspecific components. The nonspecific components act as barriers or eliminators of a wide range of pathogens ...

responses in the host that concomitantly inhibit the colonizing pathogen. An example of this has been observed with ''B. thetaiotaomicron'', which can induce the host to produce antimicrobial C-type lectins REGIIIγ and REGIIIβ, both anti-microbial peptides that target

gram-positive In bacteriology, gram-positive bacteria are bacteria that give a positive result in the Gram stain test, which is traditionally used to quickly classify bacteria into two broad categories according to their type of cell wall. Gram-positive bact ...

bacteria. Scientists found that gut infections increase its microbiota's resistance to subsequent infections, that

taurine Taurine (), or 2-aminoethanesulfonic acid, is an organic compound that is widely distributed in animal tissues. It is a major constituent of bile and can be found in the large intestine, and accounts for up to 0.1% of total human body weight. I ...

is used in as a nutrient to nourish and train the microbiota for this by potentiating its production of sulfide and that the exogenous supply of taurine can induce this microbiota alteration.

References

{{DEFAULTSORT:Colonization resistance Bacteriology Digestive system Gut flora Environmental microbiology