Identification ofPorphyromonas gingivalisandActinobacillus actinomycetemcomitansin Apical Border Plaque

Abstract

This study concerns the identification of Porphyromonas gingivalis and Actinobacillus actinomycetemcomitans in subgingival plaque close to the bottom of the pocket using the combination of ultrastructural criteria and postembedding immunogold labelling. Specimens of plaque from deep periodontal pockets were fixed in 0.5 per cent glutaraldehyde in 0.1 M sodium cacodylate buffer, dehydrated, and embedded in LR White acrylic resin. Pure cultures of P. gingivalis and A. actinomycetemcomitans were processed in the same way. Ultrastructural differences in the structure of the cell wall envelope and cytoplasm were noted between the two organisms. Similar differences were observed in certain Gram-negative organisms within the apical border plaque samples. Following immunogold labelling, cells with the same ultrastructural features as P. gingivalis or A. actinomycetemcomitans showed positive labelling. None of the other organisms in the plaque was labelled. We therefore suggest that the combination of morphological criteria and a specific marking system such as colloidal gold provides a method by which organisms in apical border plaque can be identified in situ , although differentiation between strains may as yet be more difficult. Keywords: Porphyromonas gingivalis ; Actinobacillus actinomycetemcomitans ; Periodontitis; Plaque; Ultrastructure; Immunogold.