Santoni, K.; Wong, J.; Rattle, J.; Meunier, E.; Frankel, G.

Hypervirulent Klebsiella pneumoniae (hvKp) cause invasive infections despite ro-bust neutrophil recruitment, yet the mechanisms enabling persistence in neutrophil-rich environments remain poorly defined. Here, we show that hvKp do not simply resist neutrophil antimicrobial mechanisms but instead constrain neutrophils into a neutral functional state characterised by limited bactericidal activity. Using genetic dissection of the rmpADC locus, pharmacological inhibition of neutrophil effector pathways, and analysis of a diverse panel of clinical isolates, we demonstrate that rmpADC-driven capsule properties uncouple neutrophil recognition and activation from bacterial killing. Deletion of rmpADC restores phagocytosis, degranulation, and intraphagosomal killing, whereas loss of individual rmpD or rmpC permits neu-trophil activation without bacterial killing. Moreover, hypermucoviscosity alone is sufficient to protect bacteria from neutrophil-mediated killing across multiple genetic backgrounds. Together, these findings identify capsule-driven immune state control as a central mechanism of hvKp neutrophil evasion and reveal distinct thresholds governing neutrophil activation and bactericidal outcome.