Importance of a lipopolysaccharide-containing extracellular toxic complex in infections produced by Klebsiella pneumoniae.

A Klebsiella pneumoniae serotype 2 strain was examined for its ability to produce extracellular toxic material. The organism was grown to the stationary phase in a defined medium, and the toxic material was isolated by ultrafiltration-ion-exchange chromatography on DEAE-Sephacel and gel filtration chromatography on Sepharose 4B or 2B. It was found to be comprised of 63% capsular polysaccharide, 30% lipopolysaccharide, and 7% protein and possessed a 50% lethal dose (when injected intraperitoneally into mice) of 393 +/- 45 micrograms. The toxicity appeared to be associated with the endotoxin portion of the compound, because boiling for 15 min and exposure to proteolytic enzymes had no effect on the toxicity. However, saponification destroyed the toxicity of the compound. Studies employing radial immunodiffusion examining the sera of mice infected with this organism demonstrated in vivo production of the complex at levels sufficiently high to produce death. When sublethal amounts of this complex were placed in the lungs of specific-pathogen-free mice, the lung pathology observed after 24, 48, and 72 h was similar to the damage caused by an active K. pneumoniae lobar pneumonia. These data indicate that this extracellular toxic compound produced by K. pneumoniae may be responsible for the lethality and lung tissue destruction normally associated with an active lobar pneumonia caused by this organism.