Detection of bacteria in dental samples using the Periodic acid-Schiff (PAS) histological stain

The bacterial cell wall mainly consists of glycoproteins and polysaccharides, which could be detected in dental tissue with specific stain protocols. The present study aimed to investigate bacteria stainability in dental histological samples of human teeth by a histochemical method. Eight extracted teeth, because severely decayed, were decalcified, dehydrated, paraffin-embedded, and serially sectioned at 4 µm thickness each. The serial sections were then stained with Periodic acid-Schiff (PAS). Furthermore, SEM analysis was performed on the same slide of one previously histologically investigated tooth to acquire more details on the structures stained by the PAS method obtained from the histological procedures. Afterward, some American Type Culture Collection (ATCC) strains, smeared on glass slides, were stained following the staining method used in histological samples. Stained rod and cocci forms by PAS stain, observed under light microscopy, were predominantly detected inside dentinal tubules and root canal space of histologically examined specimens, suggesting their bacterial origin. Additional SEM analysis on the identical histological stained slide showed the precise nature of these forms (bacteria) and supplemental information regarding their vitality status. In addition, ATCC smeared strain samples showed variable PAS stainability of microorganisms investigated. Due to its properties, the PAS histochemical stain could be a valid and helpful aid for non- or weakly stainable microorganisms in infected tissues to be associated with other methods of investigation.