Ruthenium red and the bacterial glycocalyx

Ruthenium red, a promising cationic reagent for electron microscopy (EM), h as long been an important tool in histology, The reagent was initially used by botanists as a semispecific stain for pectic substances, but it has gra dually been embraced by investigators in microbiology and the animal scienc es as a stain for anionic glycosylated polymeric substances. Luft developed a reliable method and demonstrated that ruthenium red was a useful reagent for visualizing ultrastructural detail. Many investigators, using modifica tions of Luft's approach, have identified numerous applications for this im portant reagent. Ruthenium red has been used to show the ultrastructural de tail of bacterial glycocalyces. Strong, sharp and consistent observations o f this ultrastructural component of the bacterial cell have given a better understanding its fibrous anionic matrix. Any variations in staining owing to artifactual alteration of the fine delicate ultrastructural features hav e been overcome by incorporation of diamine lysine into ruthenium red metho ds, thus providing flexible processing times under less than ideal laborato ry sampling conditions. Ruthenium red has broad utility in the biological s ciences, and in combination with lysine, it is an excellent EM stain for en hanced visualization of bacterial glycocalyx from culture or from clinical specimens.