Acinetobacter species secrete compounds that promote intestinal inflammation

Abstract

Background: The gut microbiota is known to impact multiple aspects of human health, including immune modulation, nutrient uptake, cell metabolism, and defense against pathogens. The composition and diversity of the gut microbiota is known to be altered in the setting of inflammatory bowel disease (IBD). IBD, which encompasses the subsets Crohn’s Disease and Ulcerative Colitis, is a life-long condition characterized by chronic inflammation of the gastrointestinal tract. It has long been speculated that gut bacteria drive or exacerbate inflammation in IBD patients, but few studies have identified bacterial candidates. Analysis of 3,853 publicly available RNA-Seq samples revealed that Acinetobacter calcoaceticus was one of the top 10 highest elevated bacteria in Crohn's Disease patients. Acinetobacter are well-characterized by their antibiotic resistance, but little is known about its relationship to the intestine. We hypothesize that A. calcoaceticus stimulates intestinal inflammation and exacerbates colitis. Materials & Results: To identify if A. calcoaceticus could stimulate inflammation, we generated inside out mouse jejunal and colonic organoids and added live A. calcoaceticus bacteria to the cultures. As a positive control, we added another Acinetobacter species A. baumannii and as a negative control, we added E. coli Nissle. After 6 hrs, we observed significant expression of pro-inflammatory cytokines in response to A. calcoaceticus and A. baumannii, while E. coli Nissle did not generate the same responses. To further investigate the compounds responsible to inflammation, we grew our bacterial strains and exposed Caenorhabditis elegans to the bacterial secreted compounds. Similar to our organoid experiments, A. calcoaceticus and A.baumannii were lethal to worms, while E. coli had no effect on C. elegans viability. Next, we sought to address the effects of Acinetoacter on the gut in vivo. We oral gavaged adult BALB/c mice with A. calcoaceticus, A. baumannii and E. coli Nissle and found that in the setting of a complex gut microbiota, these bacteria alone did not stimulation inflammation. However, supplementation of anbitioics prior to introduction of our bacteria resulted in a loss of protection and enhanced inflammation. To model IBD, we administered 2,4,6-trinitrobenzene sulfonic acid (TNBS) and induced colitis and then treated mice with our bacterial strains. We found that TNBS treated mice receiving A. calcoaceticus and A. baumannii lost more weight and had worse histological scores than mice treated with vehicle control and TNBS; indicating A. calcoaceticus worsens intestinal inflammation. Conclusions: These data show that A. calcoaceticus can promote intestinal inflammation and may be a contributing factor to the inflammation experienced by IBD patients. Funding Sources for this project include: 1T32GM132055-01, The Histochemical Society’s Cornerstone Grant and the Porter Physiology Development Fellowship. This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.