Working together: gut microbe-microbe interactions shape host inflammation.

Inflammatory bowel disease (IBD) is a debilitating disorder characterized by chronic intestinal inflammation that currently has no cure. Alterations to the composition of the gut microbiota, including reduced microbial diversity and expansion of pathobionts like Enterobacteriaceae, are implicated in IBD. While this dysbiosis has been well-documented, our understanding of the function of these microbes in the development and progression of IBD is more limited. As part of the gut microbiota, these microbes undergo complex interactions with many other microorganisms that impact the structure and function of the microbial community and the health of the host. These include competitive interactions for nutrients and space and cooperative interactions that help optimize resource utilization and microbial fitness. In this minireview, we discuss the microbe-microbe interactions that can impact host inflammation and IBD progression and treatment. Due to their association with IBD, we put special emphasis on interactions between Enterobacteriaceae and other members of the microbiota that are competitive, commensal, and mutualistic. To better understand these interactions, the signals that mediate microbial interactions are highlighted, including contact-dependent and contact-independent mechanisms. Finally, mucosal biofilms involving pathobionts are examined due to their proximity to the host and ability to influence inflammation.