OP27 Oxalyl-CoA decarboxylase is a major and specific virulence factor for Adherent Invasive Escherichia coli

Abstract

Abstract Background Adherent Invasive E. coli (AIEC) strains are found in one-third of patients with ileal Crohn’s disease (CD). To date, the bacterial genes involved in AIEC survival in the inflammatory environment are still unclear. Here, we systematically identify the genes of AIEC required for gut colonization and survival under the inflammatory conditions present in a mouse model of IBD. Methods We performed a transposon sequencing (TnSeq) approach using the laboratory strain E. coli K12 MG1655 and the AIEC strain LF82. We created two saturated Tn mutant libraries (3x105 mutant per bank) and gavaged them to mice with and without dextran-sodium sulfate (DSS)-induced colitis. We screened for essential genes for each bacterium in both conditions in the Cecum, Colon, Ileum and Jejunum. Results After High-throughput sequencing, we identified oxc gene, encoding for the oxalyl-CoA decarboxylase enzyme, as crucial for the survival of LF82 but not MG1655 in the whole gastrointestinal tract in colitis setting. To confirm our TnSeq results, the effect of oxc isogenic mutant (∆oxc) and complemented strains of LF82 and MG1655 was tested. The inflammation severity was exacerbated in mice colonized with LF82WT or the complemented strain compared to LF82∆oxc. LF82∆oxc strain load decreased after colitis induction while the LF82WT and the complemented strain persisted. In a competition between LF82 WT and ∆oxc, the WT strain was able to outcompete the ∆oxc strain. This altered ability of LF82∆oxc to colonize the gut was associated with decreased bacterial motility and flagella expression. In vitro, we found a decreased resistance of different AIEC strains to oxidative stress and acidic pH compared to a collection of commensal E. coli strains. This difference was abolished in all the ∆oxc AIEC strains we built and tested, demonstrating a crucial role for this gene in the tolerance to oxidative and acidic stress. Finally, lack of oxc also caused a reduction in survival into RAW264.7 macrophages, and an altered pro-inflammatory response of the macrophage, with a significant reduction of TNF-α levels. Conclusion oxc plays a major role in vitro and in vivo for AIEC strains but not for laboratory or commensal strains. Further studies to (i) fully explore this role and (ii) evaluate Oxc as a therapeutic target are currently under investigation.