Demonstration of pneumococcal capsule under immunoelectron microscopy

Abstract

It is challenging to demonstrate the capsule of Streptococcus　pneumoniae　(S.　pneumoniae) under immunoelectron microscopy because of the thick mucopeptide cell wall hampering proper fixation. A novel rapid freeze fixation method was established to observe the capsule of S. pneumoniae. A strain of serotype 3 of S. pneumoniae isolate was analyzed after rapid freezing. An ethanol freezing-substitution fixing method was applied and immunohistochemical staining with osmium tetroxide was tested. The capsule was confirmed using the serotype 3 specific polyclonal antibodies labeled with colloidal gold particles. To the best of our knowledge, this is the first report of S. pneumoniae capsule by immunoelectron microscope.