[Substance produced by Klebsiella pneumoniae with protects it from the bactericidal effect of normal human serum].

A Klebsiella pneumoniae culture in Fouad's chemically defined medium, which was grown from 18 to 24 hours at 37 degrees C was prepared. Bacterial cells were eliminated by centrifugation and the supernatant was sterilized by Millipore membrane filtration. A protective activity against normal human serum bactericidal effect on K. pneumoniae K-9 and K-13 was ascribed to sterile filtrate. The protective filtrate seems to be a high molecular weight substance.