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Endogenous defence against invading pathogens

Natural host microbiota provides a critical defence against infection. Understanding the mechanisms behind this host-microbiota interaction is central to health maintenance.
Endogenous defence against invading pathogens
Commensal microbiota - the non-pathogenic microorganisms found normally in the host - play a crucial role in protecting their hosts against invading pathogens. Through a process called colonisation resistance, commensal microbiota can directly compete for nutrients and colonisation sites with pathogens or limit pathogen growth by triggering immune responses. However, the precise mechanisms underlying these processes remain unclear.

Seeking to address this, the EU-funded ZEBRAPROTECT (Molecular and ecological characterisation of bacterial community-mediated protection against infection in the zebrafish) project set out to characterise the molecular and ecological mechanisms underlying protection against pathogens. For this purpose, they used zebrafish larvae as a controlled biological model challenged with infection by fish pathogens.

To confirm that the protection of conventional fish against the lethal pathogen F. columnare was due to natural larva microbiota, researchers generated bacteria-free zebrafish. Upon infection with F. columnare, they observed that these zebrafish species died and their survival depended on the prior presence of bacteria within the larvae.

To identify which microbiota species were responsible for this protective effect, scientists analysed the larva natural microbiota by culture. Next, they performed a series of experiments where they colonised larvae with either individual or a combination of microbiota species prior to exposure to F. columnare. Results indicated two different species capable of conferring protection against F. columnare and a mix of eight species that worked synergistically to provide the same effect.

Results indicated that compared to bacteria-free fish, larvae with natural microbiota induced the release of certain cytokines. This pro-inflammatory state probably helps the host prepare against the invading pathogens.

Overall, the generated knowledge on the nature of commensal-host interactions will help engineer microbiota or select host-beneficial ones as an alternative prevention strategy against infections.

Related information


Host, commensal microbiota, immune response, zebrafish, pathogen
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