Figure 1.

(a), (b) Schematic to indicate the events that contribute to Clostridium difficile infection: (a) the contributions of the pathogen to disease driven by reduced gut microbiota diversity; (b) how these contributions are minimized when a more diverse microbiota is present. (c), (d) Schematic to indicate the events that contribute to the proliferation of pathobionts (resident bacteria that can contribute to disease pathology under the appropriate altered environmental conditions) in the gut microbiota. The potential contribution of the gut microbiota, and the reduction of diversity in the microbiota in particular, is highlighted as a driver for disease to draw a comparison against C. difficile infection, using C. difficile infection as a model for disease caused by reduction in host gut-microbiota diversity.