[Characterization of a substance which protects Klebsiella pneumoniae from the bactericidal effect of normal human serum].

Chemical composition of a substance produced by Klebsiella pneumoniae which is accumulated in chemically defined medium was determined. This substance (the protective factor) protects the bacterium from being killed by normal human serum. Protective factor was treated with DNase, lysozyme and an alkaline protease. The two former enzymes did not affect the protective factor. On the other hand, when alkaline protease was used, the protective activity was totally lost. Results showed that the protective factor is a protein.