Biofilms are communities of bacteria growing attached to a surface. Biofilms are responsible for more than 80% of bacterial infections in humans. Examples of diseases caused by biofilms include Dental caries, periodontitis, cystic fibrosis pneumonia, and infective endocarditis, and infections of various medical devices such as intravenous catheters, artificial joints and contact lenses. Little is known about the detachment of bacteria from biofilms, a process necessary for the spread of infections to new sites. Biofilm detachment represents an important area of future research that is expected to lead to novel strategies for treating biofilm infections The Gram-negative oral bacterium Actinobacillus actinomycetemcomitans has been implicated as the causative agent of localized juvenile periodontitis, a severe and rapid form of periodontal disease that affects 70,000 primarily African-Americans in the U.S. annually. A. actinomycetemcomitans also causes several non-oral infections including bacteremias, brain abscesses and infective endocarditis. A striking feature of fresh clinical isolates of A. actinomycetemcomitans is their ability form extremely tenacious biofilms on surfaces such as glass, plastic and saliva-coated hydroxyapatite, a property that has been shown to be essential for virulence in a rat model. Tight adherence to surfaces also makes A. actinomycetemcomitans an excellent model for studying biofilm growth and detachment in vitro. Genetic and microscopic studies in this laboratory have shown that A. actinomycetemcomitans cells grown attached to surfaces in broth form highly-differentiated biofilm colonies that are capable of releasing cells into the medium. Biochemical and genetic studies indicate that A. actinomycetemcomitans biofilm colonies are held together by a sticky, extracellular polysaccharide. The proposed experiments are a continuation of our preliminary studies which have identified an enzyme produced by A. actinomycetemcomitans which causes the degradation of the sticky polysaccharide coating and detachment of A. actinomycetemcomitans cells from the biofilm aggregate. We plan to use genetic techniques to understand how production of this enzyme is regulated in the bacterial cell, and biochemical techniques to determine the structure of the polysaccharide substance on the surface of the cell. Preliminary data indicate that this enzyme is capable of degrading biofilms produced by other species of Gram-negative and Gram-positive bacteria, indicating that it may represent a novel anti-biofilm therapeutic with broad spectrum potential.
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