Bacterial Swarmers exhibit a Protective Response to Intestinal Stress

Bacterial swarming is a conserved and distinct form of bacterial motility that is often regulated differently than biofilm communities. While bacterial biofilms are associated with pathogenesis and pathobiology of human diseases, there are very few examples of swarming behaviors that uniquely define or align with human pathophysiology. Here we report that bacterial swarmers are associated with protection against intestinal inflammation in a murine model of acute colitis. Using feces in soft-agar plate assay, we showed bacterial spreading harboring swarmers, is highly predictive of the presence of intestinal stress in mice, pigs, and humans. From murine feces, we isolated a novel Enterobacter swarming strain, SM3, which demonstrated significant protection from intestinal inflammation when compared to its swarming deficient but swimming competent transposon mutants in a DSS-induced intestinal inflammation model of mice. Known commensal swarmers also protected against intestinal inflammation when compared to swarming deficient isogenic mutants. When treated with SM3, its anti-inflammatory properties paralleled a significant reduction of luminal oxygen concentration in colitic mice as observed in real time using a microsensor probe. This led to a favorable anaerobic environment conducive to the growth of beneficial anaerobes as demonstrated by 16S profiling of feces. This work identifies a new paradigm in which intestinal stress, specifically inflammation, allows for the emergence of swarming bacteria, which in turn can protect and heal from intestinal inflammation.