Abstract
Serotype K1 Klebsiella pneumoniae is a major cause of liver abscesses and endophthalmitis. This study was designed to identify the role of neutrophils in the development of distant metastatic complications that were caused by serotype K1 K. pneumoniae. An in vitro cellular model was used to assess serum resistance and neutrophil-mediated killing. BALB/c mice were injected with neutrophils containing phagocytosed K. pneumoniae. Serotype K1 K. pneumoniae was significantly more resistant to serum killing, neutrophil-mediated phagocytosis and intra-cellular killing than non-K1 isolates (p<0.01). Electron microscopic examination had similar findings as in the bioassay findings. Intraperitoneal injection of neutrophils containing phagocytosed serotype K1 K. pneumoniae led to abscess formation in multiple sites including the subcutaneous tissue, lung, and liver, whereas no abscess formation was observed in mice injected with non-K1 isolates. The resistance of serotype K1 K. pneumoniae to complement- and neutrophil-mediated intracellular killing results in the dissemination of K. pneumoniae via the bloodstream. Escape from neutrophil intracellular killing may contribute to the dissemination and establishment of distant metastases. Thus, neutrophils play a role as a vehicle for helping K. pneumoniae and contributing to the establishment of liver abscess and distant metastatic complications.
Highlights
Klebsiella pneumoniae is the major pathogen associated with pyogenic liver abscesses [1,2,3,4,5]
Serotype K1 was found to be more resistant to killing by both serum killing (p,0.01) (Fig. 1) and intracellular killing after neutrophil phagocytosis (p,0.01) (Fig. 2) than non-K1 serotypes in cellular and murine models
We observed that serotype K1 is the main serotype in K. pneumoniae-mediated liver abscess and is associated with the development of endophthalmitis and meningitis, in diabetic patients [2]
Summary
Klebsiella pneumoniae is the major pathogen associated with pyogenic liver abscesses [1,2,3,4,5]. Most patients with K. pneumoniae liver abscess develop bacteremia and septic metastatic complications including endophthalmitis, meningitis, brain and lung abscesses, and necrotizing fasciitis [5,6,7,8,9,10,11]. Serotype K1 is the most common serotype of K. pneumoniae isolated from the blood, urine, respiratory tract, and pus (especially from liver abscesses) in Taiwan [13]. 60–93% of patients with liver abscesses and distant metastasis of endophthalmitis were reported to be diabetic [1,2,7,11,13,14,15,16,17]
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