Adhesion of A. actinomycetemcomitans to Host Components of the Extracellular Matrix

The periodontal pocket is colonized by bacteria that exist in the dental biofilm or plaque. Apical migration of the pocket epithelium deepens the periodontal pocket. This first step is followed by the resorption of the alveolar bone, which leads initially e to tooth mobility and subsequently to tooth loss. Aggregatibacter actinomycetemcomitans, a gram-negative bacterium, localized in the periodontal pocket, is involved in causing periodontitis and other serious systemic diseases, e.g. soft abscesses, pneumonia, urinary tract infection, infective endocarditis, and the formation of atherosclerotic plaque [1]. Adhesion to host tissue, such as extracellular matrix, is considered an essential event in the pathogenic process of the infectious disease of this bacterium. SEM examination of trypsin treated rabbit mitral valves showed large numbers of A. actinomycetemcomitans (Aa) bound to the exposed collagen fibers [2]. Adhesion to collagen is mainly mediated by EmaA (Extracellular matrix protein adhesin A), which is a non fimbrial adhesin that forms antenna-like appendages on the surface of the bacteria. These appendages are absent on the surface of the emaA mutant strain, which also lacks the ability to bind collagen [3]. Complementation of the mutant strain with a plasmid containing the emaA gene restores both the surface appendages and the collagen binding activity.