Abstract
Hypervirulent Klebsiella pneumoniae (HvKP) is hypermucoviscous organism, carrying genes of rmpA and aerobactin, causing serious community-acquired infection and metastatically spread in young healthy hosts. Neutrophils play an important role during innate immune response against bacterial infection by phagocytosis and neutrophil extracellular traps (NETs). Whether neutrophils can effectively defend against HvKP remains unclear. In this study, we observed that the HvKP was significantly more resistant to neutrophil-mediated phagocytosis and intracellular killing than classic Klebsiella pneumoniae (cKP) isolates. Although both HvKP and cKP induced NETs under scanning electron microscopy and confocal microscopy, more cKP than HvKP were trapped in NETs, and the killing by intracellular and extracellular mechanisms of neutrophils was detected only on cKP. Together, our results demonstrated that HvKP resisted to both intracellular and extracellular killing of neutrophils.
Highlights
A new hypervirulent clinical variant of Klebsiella pneumoniae (HvKP) is emerging, and it has become the major pathogen associated with severe infections, such as pyogenic liver abscesses [1], pneumonia [2] and endophthalmitis [3]
The results indicated that HvKP-K1 and HvKP-K2 were more resistant to neutrophil phagocytosis compared with classic Klebsiella pneumoniae (cKP)
Neutrophils are essential effector cells of the innate immune system that are extremely important for the first-line defense against bacterial infections
Summary
A new hypervirulent clinical variant of Klebsiella pneumoniae (HvKP) is emerging, and it has become the major pathogen associated with severe infections, such as pyogenic liver abscesses [1], pneumonia [2] and endophthalmitis [3]. It has been recognized that HvKP strains exhibit enhanced virulence features including producing more capsular polysaccharide, possessing anti-phagocytosis and causing distant metastases [4,5], and are much more invasive than classic Klebsiella pneumoniae (cKP). The majority of HvKP strains causing infections belong to serotype K1 or K2 [6]. Capsular polysaccharide (CPS) from Klebsiella pneumoniae (KP) increases resistance to neutrophil phagocytosis in vitro [8]. Previous studies have shown that serotype K1 of HvKP is significantly more resistant to neutrophil-mediated phagocytosis than non-K1 isolates [5].
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