Ruthenium tetroxide fixation comparison of bacterial surface ultrastructure

Ruthenium tetroxide is known to improve overall contrast and preservation of membranes. It is a cationic dye which has an affinity for strongly positive anionic polymers and thus more effectively preserves exopolysaccharide materials such as glycocalyx on bacterial membrane surfaces. This study was undertaken to determine the usefulness of this technique over conventional fixation procedures in the study of bacterial surface structures that are important in pathogenicity. Different strains of pathogenic bacteria (possessing various surface structures) were routinely fixed in 2.5% glutareldehyde and 1% osmium tetroxide, dehydrated in a graded series of ethanols, and embedded in Epon 812 epoxy resin. Half of each sample was fixed in 0.05% ruthenium tetroxide (pH7.1) instead of osmium tetroxide, and then dehydrated and embedded as above. All of the samples were sectioned and post stained in uranyl acetate/lead citrate.