Elucidating the role of Acinetobacter calcoaceticus in promoting intestinal inflammation

Background: Inflammatory bowel disease (IBD), which encompasses the subsets Crohn’s Disease and Ulcerative Colitis, is a life-long condition characterized by chronic inflammation of the gastrointestinal tract. Multiple studies over the last decade have implicated intestinal bacteria in the initiation and perpetuation of IBD, but the precise microbes which contribute to inflammation remain unknown. Analysis of 3,853 publicly available RNA-Seq datasets from 26 independent studies 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 colonizes the gut and exacerbates intestinal inflammation. Materials & Results: To examine the ability of A. calcoaceticus to grow in the gut, we grew commercially available and clinical isolates of A. calcoaceticus in vitro in minimal media with stressors found in the gut. All strains grew in a range of pH (4-7), osmolarity (0.1-1 M NaCl), ethanol (1- 5%) and hydrogen peroxide (0.05-0.1%); indicating that A. calcoaceticus is well-adapted to withstand the harsher conditions of the gastrointestinal tract. To confirm our in vitro findings, we oral gavaged mice with A. calcoaceticus and examined fecal levels using selective agar and qPCR 7 days after gavage. We observed low levels of Acinetobacter in vehicle control mice and high levels of Acinetobacter in our mice gavaged with A. calcoaceticus (average 9.9x 107 CFU); suggesting that A. calcoaceticus readily colonizes the gut. IBD patients exhibit cycles of active inflammation, known as flares. During flares, gut microbes can participate in exacerbating the existing inflammation by continuously activating pro-inflammatory responses. To examine the ability of A. calcoaceticus to enhance inflammation, we oral gavaged mice with either a vehicle control (PBS) or A. calcoaceticus and the following day we treated mice with 2% dextran sodium sulfate (DSS) in the drinking water for 5 days to induce mild colitis. Mice treated with A. calcoaceticus and DSS lost more weight and had worse histological scores that mice treated with vehicle control and DSS; indicating A. calcoaceticus worsens intestinal inflammation. Consistent with these findings, addition of live A. calcoaceticus to inside-out-intestinal organoids stimulated the production of pro-inflammatory cytokines Tnf, IL-8, IL-1α and Mcp-1; indicating that A. calcoaceticus can drive epithelial inflammation. Conclusions: These data indicate that A. calcoaceticus can promote intestinal inflammation and maybe a contributing factor to the inflammation experienced by IBD patients. We speculate that traditional IBD treatments, such as anti-TNF therapy, could be complemented with A. calcoaceticus specific antibiotics, such as novobiocin, to alleviate inflammation and potentially improve patient well-being. This is the full abstract presented at the American Physiology Summit 2023 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.