Electron Microscopy of the Gonococcal Capsule

Strains of Neisseria gonorrhoeae grown on agar (designated 1/2 GPH) containing peptone, hemoglobin extract, Isovitalex (BBL Microbiology Systems, Cockeysville, Maryland), and 0.05% glucose were stained with Alcian blue and examined by electron microscopy. Three of five strains had capsular material surrounding the majority of organisms. Growth of organisms to log phase and fixation and staining with Alcian blue-glutaraldehyde on the agar surface before manipulation of the organisms were important variables for the morphologic demonstration of intact capsules. Two of the three strains that were encapsulated when grown on 1/2 GPH agar were poorly encapsulated when grown on a standard gonococcal agar. Gentle washing of encapsulated organisms before fixation removed most of the capsular material. The gonococcal capsule stained with ruthenium red, which suggested that it was composed of acidic polysaccharide. Visualization of capsules on both N. gonorrhoeae and Neisseria meningitidis with ruthenium red was not as consistent as with Alcian blue, presumably because Alcian blue-glutaraldehyde not only stains but also fixes the polysaccharide.