Electron microscopic demonstration of bacterial lipopolysaccharides in dental plaque matrix

abstract – Bacterial lipopolysaccharide endotoxins (LPS) obtained by phenol-water extraction from oral strains of Bacteroides melaninogenicus and Fusobacterium were studied in the electron microscope. The LPS particles had a characteristic morphology comparable to that of LPS from other Gram-negative microorganisms. The LPS appeared as circular structures or discs delimited by single or trilaminar membranes, or as short rods composed of two electron-dense membranes separated by a fine, less-dense layer. Teeth with adhering soft and calcified bacterial plaque, which were extracted because of advanced periodontal disease, were obtained and processed for electron microscopy. Close examination of thin sections revealed an abundance of particles in the dental plaque which closely resembled those found in LPS preparations of Gram-negative oral microorganisms. Circular as well as rod-like particles were, identified. These particles, which were most frequent in regions containing Gram-negative bacteria, were distinctly different from the granular, filamentous, and other structures previously reported in the intercellular matrix of the dental plaque. It was concluded that the circular and rod-like structures described represent free bacterial lipopolysaccharide. LPS particles were found superficially in the plaque as well as in deeper layers and in regions undergoing calcification. In regions containing Gram-negative bacteria, intercellular mineral deposition often occurred in close association with the LPS particles.