title: Capsular polysaccharide is a major complement resistance factor in lipopolysaccharide O side chain-deficient Klebsiella pneumoniae clinical isolates.
abstract: We have previously demonstrated the existence of Klebsiella pneumoniae clinical isolates deficient in the lipopolysaccharide O side chain, the major factor for resistance to complement-mediated killing in this bacterial species. These isolates are complement resistant, and their mechanisms to resist complement were investigated by selecting transposon-generated complement-sensitive mutants. One mutant with a drastically reduced capacity to grow in nonimmune human serum carried the transposon inserted in an open reading frame of a gene cluster involved in capsule synthesis. This mutant produced less capsule, bound more molecules of the complement component C3, and was more sensitive to complement-mediated and opsonophagocytic killings than was the parent strain. Four additional clinical isolates representing four different K serotypes were studied, and results showed that capsular polysaccharide is a major complement resistance factor in these O side chain-deficient isolates.
authors.affiliation: Unidad de Investigación, Hospital Universitario de Son Dureta, Palma de Mallorca, Spain.
authors.forename: D
authors.initials: D
authors.lastname: Alvarez
authors.forename: S
authors.initials: S
authors.lastname: Merino
authors.forename: J M
authors.initials: JM
authors.lastname: Tomás
authors.forename: V J
authors.initials: VJ
authors.lastname: Benedí
authors.forename: S
authors.initials: S
authors.lastname: Albertí
mesh_terms: D016667:Bacterial Capsules / Q000502:physiology*; D001770:Blood Bactericidal Activity; D003165:Complement System Proteins / Q000276:immunology*; D006801:Humans; D007711:Klebsiella pneumoniae / Q000276:immunology*; D019081:O Antigens / Q000502:physiology*; D010587:Phagocytosis; D011135:Polysaccharides, Bacterial / Q000502:physiology*
chemical_list: D019081:O Antigens; D011135:Polysaccharides, Bacterial; D003165:Complement System Proteins