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

ORIGINAL IMAGE FILES<b><br></b><b>Abstract</b> Background: Hypervirulent <i>Klebsiella pneumoniae</i> (hv<i>Kp</i>) 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 <i>K. pneumoniae</i> strains (non-hv<i>Kp</i>), including lineages which have acquired carbapenem resistance (CR<i>Kp</i>), 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 hv<i>Kp</i> infections. Methods: To study the pathophysiology of abscess formation, mice were infected intravenously with hv<i>Kp</i> and non-hv<i>Kp </i>isolates and intracellular bacterial replication and neutrophil influx in liver and spleen was quantified by fluorescence microscopy. Microbiological and microscopy analysis of an <i>ex vivo </i>model of porcine liver and spleen infection was used to confirm within-macrophage replication. Findings: We demonstrate that hv<i>Kp </i>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-hv<i>Kp </i>were efficiently cleared. hv<i>Kp</i> 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 hv<i>Kp </i>to replicate within the hepatic macrophages. Intepretation: These findings demonstrate subversion of innate immune processes in the liver by <i>Kp</i> and resistance to Kupffer cell mediated clearance as an explanation for the propensity of hv<i>Kp </i>strains<i> </i>to cause hepatic abscesses.<br>