Figure 2.

Microbiological and immunological defense against CDI. (Left): Colonization is established in early infancy but regresses in the first year of life with both the maturation of the immune system and the development of the full microbiome. (Middle): In children and young adults the immune system is balanced and the microbiome intact. Both factors control growth of C. diffcile and toxin production. (Right): In the elderly population the microbiome and the immune system are both subject to age-related changes, which leads to increased susceptibility for CDI. Treatment with antibiotics results in reduction of microbiota and dysbiosis and enables growth of C. difficile. Loss of microbiota-mediated stimulation of immune cells leads to loss of IgA secretion and Treg and thereby facilitates CDI and the associated inflammatory processes. Therapeutic options are provided below the panels.