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.
This study demonstrates the probiotic potential of colonization with non‐toxigenic Bacteroides fragilis, protecting the host from enterotoxigenic B. fragilis‐induced disease through intraspecific competition via type VI secretion.
Non‐toxigenic Bacteroides fragilis outcompetes enterotoxigenic B. fragilis during mouse colonization through type VI secretion.
A differentially encoded effector–immunity pair dictates strain dominance in vivo.
Colonization resistance against enterotoxigenic B. fragilis is strain‐specific.
Restriction of enterotoxigenic B. fragilis colonization through competition with a non‐toxigenic strain prevents disease in a murine host.
- Received February 25, 2016.
- Revision received June 18, 2016.
- Accepted June 21, 2016.
- © 2016 The Authors