Adherence of Aggregatibacter actinomycetemcomitans via serotype-specific polysaccharide antigens in lipopolysaccharides

Introduction: Gram‐negative Aggregatibacter actinomycetemcomitans is recognized as an important periodontal pathogen. A striking property of this bacterium is its ability to form a tenacious biofilm adhering to abiotic surfaces. Both fimbrial and non‐fimbrial adhesins are believed to be responsible for this ability. In our study, specific markerless mutants in the biosynthesis genes of cell surface polysaccharides were constructed with the Cre‐loxP recombination system to identify non‐fimbrial adhesin(s). Methods: Non‐fimbriated A. actinomycetemcomitans strain ATCC29523 (serotype a) was used to construct a deletion mutant of serotype‐a specific polysaccharide antigen (SPA‐a) in lipopolysaccharide (LPS). The LPS was purified through a polymyxin B column following phenol extraction, and verified by silver staining following sodium dodecyl sulfate–polyacrylamide gel electrophoresis and by immunoblot analysis using rabbit antisera raised against SPA‐a. Strains were grown in broth for 2 days and examined for the adherence of bacterial cells on the glass surface. Results: Strain ATCC29523 formed a thin film of bacterial growth on the glass surface. The deletion of SPA‐a affected its ability to form this thin film. When this mutant was rescued with the wild‐type SPA‐a gene cluster, its adherence‐positive phenotype was restored. Conclusion: SPA‐a in the LPS molecule appears to promote the adherence of A. actinomycetemcomitans cells to abiotic surfaces.