Colonization resistance is the mechanism whereby the
intestinal microbiota protects itself against incursion by new and often harmful
microorganisms
A microorganism, or microbe,, ''mikros'', "small") and ''organism'' from the el, ὀργανισμός, ''organismós'', "organism"). It is usually written as a single word but is sometimes hyphenated (''micro-organism''), especially in olde ...
.
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 were susceptible to ''
Salmonella enterica'' 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
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 ...
.
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'' for
carbohydrates
In organic chemistry, a carbohydrate () is a biomolecule consisting of carbon (C), hydrogen (H) and oxygen (O) atoms, usually with a hydrogen–oxygen atom ratio of 2:1 (as in water) and thus with the empirical formula (where ''m'' may or may ...
in the
intestinal lumen) or by producing growth inhibitors (e.g. ''Bacteroides thuringiensis'' can secrete
bacteriocin that directly targets spore-forming ''
Clostridium difficile
''Clostridioides difficile'' (syn. ''Clostridium difficile'') is a bacterium that is well known for causing serious diarrheal infections, and may also cause colon cancer. Also known as ''C. difficile'', or ''C. diff'' (), is Gram-positive spec ...
'', 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 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 bacteria.
Scientists found that gut infections increase its microbiota's resistance to subsequent infections, that
taurine 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