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.

FIG. 1

SDS-PAGE analysis and silver staining of purified LPS (50 ng) from K. pneumoniae strains grown overnight at 37°C in 25% NHS. Lanes correspond, from left to right, to LPS extracted from strains C3 (O1:K66), KD57 (O⁻:K2), KD341 (O⁻:K3), M9844/93 (O⁻:K47), USA0352/78 (O⁻:K47), and USA1555 (O⁻:K35).