Aerobactin is a key driver of hypervirulent Klebsiella pneumoniae translocation and virulence.

Hypervirulent Klebsiella pneumoniae (hvKP) is an emerging pathotype capable of causing severe systemic infections. Gastrointestinal (GI) colonization often precedes invasive disease, but the mechanisms driving translocation to extra-intestinal sites are not known. A hallmark of hvKP is a large virulence plasmid encoding a number of virulence factors, including aerobactin, a siderophore associated with enhanced virulence. Using a murine GI colonization model with an intact microbiota, we examined if aerobactin enabled hvKP to translocate, by comparing an hvKP clinical isolate (hvKP1) to an isogenic aerobactin biosynthesis mutant (iucA-). Both strains colonized the GI tract similarly, but mice colonized with the iucA- mutant exhibited significantly lower bacterial burdens in the extra-intestinal organs, indicating a defect in translocation. This defect was not observed in a systemic infection model, suggesting a specific role for aerobactin in GI translocation. In cell culture based assays, the iucA- mutant showed reduced adhesion, invasion, and translocation. Both in vivo and in vitro data supported a transcellular route of translocation. Notably, the iucA- mutant displayed increased hypermucoviscosity (HMV) linked to the upregulation of the rmp locus, likely impairing host cell adhesion. These findings demonstrate that tight regulation of HMV through metal homeostasis mediated by aerobactin, promotes hvKP translocation across the intestinal epithelium by enhancing adhesion and cellular entry. This work offers new insight into hvKP pathogenesis and informs potential strategies to limit its invasive potential.