Commensal bacteria mediated defenses against pathogens

Abstract

Commensal bacterial communities residing within the intestinal lumen of mammals have evolved to flourish in this microenvironment. To preserve this niche, commensal bacteria act with the host to prevent colonization by invasive pathogens that induce inflammation and disrupt the intestinal niche commensal bacteria occupy. Thus, it is mutually beneficial to the host and commensal bacteria to inhibit a pathogen's ability to establish an infection. Commensal bacteria express factors that support colonization, maximize nutrient uptake, and produce metabolites that confer a survival advantage over pathogens. Further, commensal bacteria stimulate the host's immune defenses and drive tonic expression of anti-microbial factors. In combination, these mechanisms preserve the niche for commensal bacteria and assist the host in preventing infection.

Figure 1

Commensal bacteria-mediated mechanisms of protection against intestinal pathogens. (1) Commensal bacterial communities consume nutrients and energy sources, depriving pathogens of their niche. (2) Microbiota-derived metabolic byproducts directly inhibit pathogens. (3) Commensal bacteria stimulate host immune cells and drive basal expression of host defense factors.