Capsular polysaccharide is a major complement resistance factor in lipopolysaccharide O side chain-deficient Klebsiella pneumoniae clinical isolates

• Published in: Infection and immunity 2000-02, Vol.68 (2), p.953-955
• Main Authors: ALVAREZ, D, MERINO, S, TOMAS, J. M, BENEDI, V. J, ALBERTI, S
• Format: Article
• Language: English
• Subjects: Bacterial Capsules - physiology; Bacteriology; Biological and medical sciences; Blood Bactericidal Activity; Complement System Proteins - immunology; Fundamental and applied biological sciences. Psychology; Humans; Klebsiella pneumoniae - immunology; Microbiology; Molecular and Cellular Pathogenesis; O Antigens - physiology; Pathogenicity, virulence, toxins, bacteriocins, pyrogens, host-bacteria relations, miscellaneous strains; Phagocytosis; Polysaccharides, Bacterial - physiology
• ISSN: 0019-9567; 1098-5522
• DOI: 10.1128/IAI.68.2.953-955.2000

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.