Role of Exopolysaccharide in Aggregatibacter actinomycetemcomitans–Induced Bone Resorption in a Rat Model for Periodontal Disease

Abstract

Aggregatibacter actinomycetemcomitans a causative agent of periodontal disease in humans, forms biofilm on biotic and abiotic surfaces. A. actinomycetemcomitans biofilm is heterogeneous in nature and is composed of proteins, extracellular DNA and exopolysaccharide. To explore the role played by the exopolysaccharide in the colonization and disease progression, we employed genetic reduction approach using our rat model of A. actinomycetemcomitans-induced periodontitis. To this end, a genetically modified strain of A. actinomycetemcomitans lacking the pga operon was compared with the wild-type strain in the rat infection model. The parent and mutant strains were primarily evaluated for bone resorption and disease. Our study showed that colonization, bone resorption/disease and antibody response were all elevated in the wild-type fed rats. The bone resorption/disease caused by the pga mutant strain, lacking the exopolysaccharide, was significantly less (P < 0.05) than the bone resorption/disease caused by the wild-type strain. Further analysis of the expression levels of selected virulence genes through RT-PCR showed that the decrease in colonization, bone resorption and antibody titer in the absence of the exopolysaccharide might be due to attenuated levels of colonization genes, flp-1, apiA and aae in the mutant strain. This study demonstrates that the effect exerted by the exopolysaccharide in A. actinomycetemcomitans-induced bone resorption has hitherto not been recognized and underscores the role played by the exopolysaccharide in A. actinomycetemcomitans-induced disease.

Aggregatibacter actinomycetemcomitans, a potent immunoregulator of the periodontal host defense system and alveolar bone homeostasis

“…Notably, it was clearly shown that periodontal disease induces catabolic effects on alveolar bone homeostasis that are secondary to not only an increase in bone resorption, but also a decrease in bone formation (Baron & Saffar, ). Aggregatibacter actinomycetemcomitans LPS, leukotoxin, and to a lesser extent CdtB, PGA, and outer membrane protein 29 (OMP29) are virulence factors that have been shown to promote bone loss in preclinical rat models (Rogers et al ., ; Li et al ., ; Lin et al ., ; Yu et al ., ; Schreiner et al ., ; Shanmugam et al ., ).…”

Options and Limitations in Clinical Investigation of Bacterial Biofilms

“…A murine periodontitis model combined with genomics and quantitative PCR was used to examine the role of host factors in persistent subgingival biofilms (336). Likewise, a rat model of A. actinomycetemcomitans-induced periodontitis was combined with RT-PCR for versatile applications, ranging from genetic reduction to therapeutic efficacy evaluation according to exopolysaccharide variations (367). Another rat model, the in vivo extraradicular biofilm model, is more inclusive, as it may facilitate identification and quantification of biofilm-forming bacteria by use of real-time PCR (rt-PCR) and micro-computed tomography (368).…”

Evidence of the presence of nucleic acids and β-glucan in the matrix of non-typeable Haemophilus influenzae in vitro biofilms

“…It has been shown, however, that Histophilus somni , a relative of H. influenzae , synthesizes an exopolysaccharide composed of a D-mannan polymer and with occasional Gal residues present on side chains during biofilm formation50, although the glycosyltrasferase(s) responsible for its synthesis has not been identified. Aggregatibacter actinomycetemcomitans , another member of Pasteurellaceae, also forms biofilms containing an extracellular homopolymer of N -acetylglucosamine residues in β(1 → 6) linkage that acts as an important virulence factor51.…”