112 Scopus citations


The microbiota is a major source of protection against intestinal pathogens; however, the specific bacteria and underlying mechanisms involved are not well understood. As a model of this interaction, we sought to determine whether colonization of the murine host with symbiotic non-toxigenic Bacteroides fragilis could limit acquisition of pathogenic enterotoxigenic B. fragilis. We observed strain-specific competition with toxigenic B. fragilis, dependent upon type VI secretion, identifying an effector–immunity pair that confers pathogen exclusion. Resistance against host acquisition of a second non-toxigenic strain was also uncovered, revealing a broader function of type VI secretion systems in determining microbiota composition. The competitive exclusion of enterotoxigenic B. fragilis by a non-toxigenic strain limited toxin exposure and protected the host against intestinal inflammatory disease. Our studies demonstrate a novel role of type VI secretion systems in colonization resistance against a pathogen. This understanding of bacterial competition may be utilized to define a molecularly targeted probiotic strategy.

Original languageEnglish
Pages (from-to)1281-1291
Number of pages11
JournalEMBO Reports
Issue number9
StatePublished - Sep 1 2016


  • colonization resistance
  • enterotoxigenic Bacteroides fragilis
  • in vivo strain competition
  • probiotics
  • type VI secretion


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