Antagonism toward the intestinal microbiota and its effect on virulence.

The bacterial type VI secretion system (T6SS) is a nanomachine that delivers toxic effector proteins into target cells, killing them. In mice, we found that the T6SS attacks members of the host commensal microbiota in vivo, facilitating the pathogen's colonization of the gut. This microbial antagonistic interaction drives measurable changes in the pathogenicity of through enhanced intestinal colonization, expression of bacterial virulence genes, and activation of host innate immune genes. Because ablation of mouse commensals by this enteric pathogen correlated with more severe diarrheal symptoms, we conclude that antagonism toward the gut microbiota could improve the fitness of as a pathogen by elevating its transmission to new susceptible hosts.