Abstract
SummaryBackgroundHypervirulent 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 that have acquired carbapenem resistance, do not manifest this pathology. In this work we aimed to test the hypothesis that within-macrophage replication is a key mechanism underpinning abscess formation in hvKp infections.MethodsIn this exploratory investigation, to study the pathophysiology of abscess formation, mice were intravenously infected with 106 colony forming units (CFU) of either hvKp isolates (six strains) or non-hvKp isolates (seven strains). Intracellular bacterial replication and neutrophil influx in liver and spleen was quantified by fluorescence microscopy of sliced cryopreserved organs of mice collected 30 min, 6 h, and 24 h after infection with the aim to provide data of bacterial association to Kupffer cells in the liver and to the different tissue macrophages in the spleen. Microbiological and microscopy analysis of an ex-vivo model of pig liver and spleen infection were used to confirm within-macrophage replication. Pig organs were perfused with heparinised, autologous pig's blood and injected with 6·5 × 107 CFU of hvKp K2 sequence type 25 strain GMR151. Blood and tissue biopsies collected before infection and 30 min, 1 h, 2 h, 3 h, 4 h, and 5 h after infection were used to measure bacterial counts and to identify the subcellular localisation of bacteria by immunohistochemistry analysis.FindingsWe show that hvKp resisted phagocyte-mediated clearance and replicated in mouse liver macrophages to form clusters 6 h after infection, with a mean of 7·0 bacteria per Kupffer cell (SD 6·2); however, non-hvKp were efficiently cleared (mean 1·5 bacteria per cell [SD 1·1]). HvKp infection promoted neutrophil recruitment to sites of infection, which in the liver resulted in histopathological signs of abscess formation as early as 24 h post-infection. Experiments in pig organs which share a high functional and anatomical resemblance to human organs, provided strong evidence for the propensity of hvKp to replicate within the hepatic macrophages.InterpretationThese findings show subversion of innate immune processes in the liver by K pneumoniae and resistance to Kupffer cell mediated clearance as an explanation for the propensity of hvKp strains to cause hepatic abscesses.FundingUniversity of Oxford and a Royal Society Wolfson grant funded biosafety facility.
Highlights
Klebsiella pneumoniae invasive liver abscess syndrome is an emerging, life-threatening disease that is very difficult to manage clinically and surgically.[1]
Higher resolution confocal microscopy allowed quanti fication of the number of bacteria associated with each Kupffer cell
Microscopy data showed that clusters of bacteria were always monochrome, indicating a monoclonal infection localised to macrop hages, providing a strong indication for bacterial intracellular replication
Summary
Klebsiella pneumoniae invasive (pyogenic) liver abscess syndrome is an emerging, life-threatening disease that is very difficult to manage clinically and surgically.[1] Since its initial description in Taiwan approximately 30 years ago,[2] K pneumoniae has become the primary reported cause of pyogenic liver abscess in Asia, the USA, and Europe.[3]. K pneumoniae is a Gram-negative pathogen remarkably resistant to antibiotic therapy in the clinic. Two groups of strains pose distinct clinical problems; hypervirulent-hypermucoid lineages (hvKp) cause severe systemic infection associated with liver abscesses and additional metastatic complications[4] even in healthy populations, whereas the non-hypervirulent lineages (non-hvKp) mostly cause urinary and lower respiratory tract infections and bacteraemia in compro mised hosts. Resistance to antibiotics has spread in K pneumoniae, especially among non-hvKp, and carbapenem-resistant strains are currently among the most challenging pathogens to treat.[5,6] Despite the burden of K pneumoniae disease, there is very limited understanding of its pathogenesis, regarding tissue and cellular tropism
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
