A Morphometric Electron Microscopic Comparison of Capsules Among Fresh Clinical Isolates and Laboratory Strains ofPorphyromonas gingivalis

Abstract

Capsules of Porphyromonas gingivalis were quantitatively compared among six fresh clinical isolates from 7-10 mm periodontal pockets and four laboratory strains. Cells were harvested from either broths or solid agar surfaces. Brothgrown organisms were fixed with glutaraldehyde either directly in the growth medium or after the cells were harvested and washed. Capsules were enhanced by staining with ruthenium red. Thin sections stained with uranyl acetate and lead citrate were examined by transmission electron microscopy and the thickness of the capsule layer recorded. Morphological differences were noted in capsular layers among strains with respect to electron density and uniformity of surface coverage. However, such morphologic differences did not distinguish between fresh clinical isolates and laboratory strains. No marked differences were noted among broth- or surface-grown cells from either fresh clinical isolates or laboratory strains. Similarly, fixation of cells directly in growth medium or after harvesting and washing had no effect on capsule appearance or amount. Finally, although individual differenccs were noted among strains, no significant difference ( P = 0.180, df= 960) was noted in capsulation between fresh clinical isolates (limited passagc number) and laboratory strains of P. gingivalis . Keywords: Porphyromonas; Periodontal; Bacterial; Capsules; Clinical; Microscopy.