Carbapenem-resistant <i>Enterobacter hormaechei</i> uses mucus metabolism to facilitate gastrointestinal colonization

The emergence and global spread of carbapenem-resistant <i>Enterobacter cloacae</i> complex species present a pressing public health challenge. Carbapenem-resistant <i>Enterobacter</i> spp. cause a wide variety of infections, including septic shock fatalities in newborns and immunocompromised adults. The intestine may be a major reservoir for these resistant strains, either by facilitating contamination of fomites and transfer to susceptible individuals, or through translocation from the gut to the bloodstream. For this reason, we sought to establish a neonatal mouse model to investigate the mechanisms underpinning gut colonization by carbapenem-resistant <i>Enterobacter hormaechei</i>. We describe a new mouse model to study gut colonization by <i>Enterobacter</i> spp., leading to vital insights into the adaptation of carbapenem-resistant <i>E. hormaechei</i> to the gut environment during the early stages of intestinal colonization. We observed successful colonization and proliferation of <i>E. hormaechei</i> in the 5-day-old infant mouse gut, with primary localization to the colon following oral inoculation. We also uncovered evidence that <i>E. hormaechei</i> uses mucus as a carbon source during colonization of the colon. Our findings underscore the importance of oxygen-dependent metabolic pathways, including the pyruvate dehydrogenase complex and <i>N-</i>acetyl-D-glucosamine metabolism, in gut colonization and proliferation, which aligns with previous human studies. These insights are essential for developing novel therapeutic strategies that can serve as decolonization therapies in at-risk populations.IMPORTANCEBloodstream infections caused by <i>Enterobacter</i> spp. pose a significant clinical threat. The intestine acts as the primary site for colonization and serves as a reservoir for infection. To combat this pathogen, it is crucial to understand how carbapenem-resistant <i>Enterobacter</i> spp. colonize the gut, as such knowledge can pave the way for alternative therapeutic targets. In this study, we developed a novel neonatal mouse model for gastrointestinal colonization by <i>Enterobacter</i> spp. and discovered that mucus plays a key role as a carbon source during colonization. Additionally, we identified two mucus catabolism pathways that contribute to intestinal colonization by carbapenem-resistant <i>E. hormaechei</i>. This new mouse model offers valuable insights into host-pathogen interactions and helps identify critical gastrointestinal fitness factors of <i>Enterobacter</i>, potentially guiding the development of vaccines and alternative therapeutic strategies to minimize intestinal carriage in patient populations at risk of infection with <i>Enterobacter</i> spp.