title: Sialic acid involved in hypermucoviscosity phenotype of Klebsiella pneumoniae and associated with resistance to neutrophil phagocytosis.
abstract: Klebsiella pneumoniae (KP) with the hypermucoviscosity (HV) phenotype has abundant capsular polysaccharides (CPS) and usually causes an invasive syndrome. Sialic acid (Sia), a component of CPS in KP strains with the HV phenotype, may be anti-phagocytic. Sia-binding immunoglobulin-like lectin-9 (Siglec-9) act as an MHC class-I receptor on neutrophils that recognizes Sia and sends a signal to dampen inflammatory response. Three clinical KP strains with KP-M1 (HV-positive; capsular serotype K1), KP-14 (HV-negative; capsular serotype non-K1/K2), and DT-X (HV-negative; capsular serotype K1) were studied. We assessed total Sia in CPS extracts using enzymatic methods and phagocytosis by neutrophils of neuraminidase-treated bacteria using flow cytometry. Neutrophil killing was evaluated in the presence and absence of antibodies against Siglec-9. The concentration of Sia was significantly higher in the CPS extract of KP-M1 (56.75 ± 6.75 μmole/10(9) cfu) than in the CPS extract of KP-14 (0.02 ± 0.01 μmole/10(9) cfu) and DT-X (a negligible value). The KP-M1 (compared with the KP-14 and DT-X) was more resistant to neutrophil phagocytosis. Both the HV phenotype and resistance to phagocytosis of KP-M1 were significantly decreased after Sia removal with neuraminidase treatment. Fluorescence microscopy with an antibody against human Siglec-9 showed attachment of KP-M1 (but were absent of KP-14 and DT-X) to the surface of neutrophils and colocalization with human Siglec-9. Engagement of Siglec-9 via Sia enhanced neutrophils killing of KP-M1 by ex vivo human neutrophils bactericidal activity assay. The result showed that Sia might be a constituent of KP-M1 CPS responsible for HV, thereby contributing to anti-phagocytic activity of this pathogen.
authors.affiliation: Division of Infectious Diseases; Kaohsiung Chang Gung Memorial Hospital; Kaohsiung, Taiwan; Institute of Clinical Medical Sciences; Chang Gung University College of Medicine; Kaohsiung, Taiwan; Department of Medical Research; Kaohsiung Chang Gung Memorial Hospital; Kaohsiung, Taiwan.
authors.forename: Chen-Hsiang
authors.initials: CH
authors.lastname: Lee
authors.affiliation: Division of Infectious Diseases; Kaohsiung Chang Gung Memorial Hospital; Kaohsiung, Taiwan.
authors.forename: Chia-Chi
authors.initials: CC
authors.lastname: Chang
authors.affiliation: Division of Infectious Diseases; Kaohsiung Chang Gung Memorial Hospital; Kaohsiung, Taiwan.
authors.forename: Jien-Wei
authors.initials: JW
authors.lastname: Liu
authors.affiliation: Department of Medical Research and Development; Show Chwan Memorial Hospital; Changhua, Taiwan.
authors.forename: Rong-Fu
authors.initials: RF
authors.lastname: Chen
authors.affiliation: Institute of Clinical Medical Sciences; Chang Gung University College of Medicine; Kaohsiung, Taiwan; Department of Medical Research and Development; Show Chwan Memorial Hospital; Changhua, Taiwan.
authors.forename: Kuender D
authors.initials: KD
authors.lastname: Yang
mesh_terms: D016667:Bacterial Capsules / Q000737:chemistry / Q000276:immunology* / Q000378:metabolism; D002478:Cells, Cultured; D006801:Humans; D007711:Klebsiella pneumoniae / Q000276:immunology*; D050296:Microbial Viability; D019158:N-Acetylneuraminic Acid / Q000276:immunology* / Q000378:metabolism; D009504:Neutrophils / Q000187:drug effects* / Q000276:immunology*; D010587:Phagocytosis / Q000187:drug effects*
chemical_list: D019158:N-Acetylneuraminic Acid
keywords: K. pneumoniae; hypermucoviscosity; neutrophil; phagocytosis; sialic acid
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