Interaction of Klebsiella pneumoniae with tissue macrophages in a murine infection model and ex-vivo porcine organ perfusions: an exploratory investigation. 2021 Lancet Microbe - Original Images and Data Files

Abstract

Background: Hypervirulent Klebsiella pneumoniae (hvKp) strains of capsule type K1 and K2 cause invasive infections associated with hepatic abscesses, which can be difficult to treat and are frequently associated with relapsing infections. Other K. pneumoniae strains (non-hvKp), including lineages which have acquired carbapenem resistance (CRKp), do not manifest this pathology. In this work we aimed to test the hypothesis that within-macrophage replication is a key mechanisms underpinning abscess formation in hvKp infections.

Methods: To study the pathophysiology of abscess formation, mice were infected intravenously with hvKp and non-hvKp isolates and intracellular bacterial replication and neutrophil influx in liver and spleen was quantified by fluorescence microscopy. Microbiological and microscopy analysis of an ex vivo model of porcine liver and spleen infection was used to confirm within-macrophage replication.

Findings: We demonstrate that hvKp resisted phagocyte-mediated clearance and replicated in murine liver macrophages to form already 8 hours post challenge clusters with an average of 7.0 bacteria per cell (SD 6.1), whilst non-hvKp were efficiently cleared. hvKp infection promoted neutrophil recruitment to sites of infection, which in the liver resulted in histopathological signs of abscess formation of as early as 24h post-infection. Experiments in porcine organs, which share a high functional and anatomical resemblance to human organs, provided strong evidence for the prospensity of hvKp to replicate within the hepatic macrophages.

Intepretation: These findings demonstrate subversion of innate immune processes in the liver by Kp and resistance to Kupffer cell mediated clearance as an explanation for the propensity of hvKp strains to cause hepatic abscesses.