Electronmicroscopic finding of surface structure and capsular swelling reaction of a strain of Klebsiella pneumoniae

To investigate a capsular swelling reaction of the strain K-9 of Klebsiella pneumoniae, possessor of large capsule, ultra-thin sections of the organisms were stained with uranyl acetate and lead citrate and were treated with rabbit antiserum. The ultra-thin sections of above stained organisms showed spike-like structure in outmost layer of the cell wall. When they were treated with rabbit antiserum, the outmost layers of the organisms was surrounded by a zone of oval to round polymorphous vesicular structure which covered the spike-like appendages. These findings were assumed being capsular swelling reaction of these organisms. However, when they were treated with rabbit antiserum which was previously absorbed with the polysaccharide surface antigen, polymorphous vesicular structures did not appear and sharp spiked structures issuing from the cell wall were exposed.