The pathogenicity of Klebsiella pneumoniae for mice: the relationship to the quantity and rate of production of type-specific capsular polysaccharide.

It is well established that among certain groups of microorganisms the presence of a capsule is essential for virulence; these studies are largely limited to all-or-none effects, i. e. the presence or absence of capsule. Among a few species, e. g. Diplococcus pneumoniae, some quantitative studies have been made which indicate that there is a relationship between size of capsule and degree of pathogenicity (Shaffer et al., 1936; Rich and McKee, 1936; MacLeod and Kraus, 1950). In an attempt to extend to organisms other than the pneumococcus the quantitative studies of the relationship of capsule size to pathogenicity, 4 strains of Klebsiella pneumoniae type 2 were investigated. While it was found that to some extent the pathogenicity for mice was influenced by capsule size, the rate of capsule production also proved to be a determining factor.