Effect of Capsular Polysaccharide of Klebsiella pneumoniae on Host Resistance to Bacterial Infections

Open Access
Publisher Website
Google Scholar
Abstract
When Klebsiella pneumoniae capsular polysaccharide (CPS‐K) from type 1, Kasuya strain, was injected intraperitoneally (i.p.) immediately before i.p. bacterial challenge, the survival time of mice infected with Salmonella enteritidis NUB 1 (virulent strain) was shortened and the mortality rate for mice infected with S. enteritidis NUB 31 (avirulent strain) was enhanced. The promotion of infection with S. enteritidis NUB 1 by CPS‐K depended upon its dose, the effect of CPS‐K being demonstrable up to as little as 0.2 μg per mouse. In the case of S. enteritidis NUB 31, the effect of CPS‐K was detectable only when more than 20 μg per mouse was injected. As a result of enumeration of bacterial populations in the peritoneal washing, blood, liver and spleen, it was revealed that CPS‐K promoted in vivo growth of S. enteritidis NUB 1 and NUB 31. In addition, CPS‐K enhanced the mortality rate in mice infected with Streptococcus pyogenes or Streptococcus pneumoniae. The peak CPS‐K effect on infection with S. enteritidis NUB 1 was seen when given immediately before bacterial challenge. The active substance responsible for the infection‐promoting effect of CPS‐K was neutral CPS‐K, which is distinct from the O antigen and from acidic CPS‐K (the type‐specific capsular antigen). Preparations of neutral CPS‐K isolated from the other three strains of K. pneumoniae exhibited a marked infection‐promoting effect comparable with that of preparations from the Kasuya strain. Neutral CPS‐K, with identical antigenicity to that from the Kasuya strain, has already been found to exert a strong adjuvant effect on antibody responses to various antigens in mice. No parallelism exists between infection‐promoting activity and adjuvant activity of neutral CPS‐K.