The broad, long-term objectives of this research are to understand the molecular, biochemical, and immunologic basis of the pathogenesis of coagulase-negative staphylococcal infections associated with foreign bodies that are used commonly in contemporary clinical practice. The molecular and biochemical focus will be on the capsular polysaccharide/adhesion (PS/A) molecule involved in adherence of coagulase-negative staphylococci to synthetic materials. We will study the organization and linkages of monosaccharide components of PS/A to determine structures which are critical for mediating adherence to catheters, and visualize PS/A in situ from infected catheters using scanning electron microscopy and monoclonal antibodies. A range of clinical isolates of coagulase-negative staphylococci will be screened for the existence of alternative PS/A-like adhesions using immune electron microscopy. We will utilize our rabbit model of catheter-related infection along with strains of coagulase- negative staphylococci which differ in the expression of PS/A and elaboration of slime to study the relative roles of PS/A and slime in the pathogenesis of catheter colonization and bloodstream invasion. In addition we will study host factors and clinical interventions which might enhance the risk of colonization and infection with coagulase-negative staphylococci. This area of inquiry was suggested by recent epidemiologic investigations which strongly implicate intravenous administration of lipid emulsions as a major co-factor in dramatically increasing the risk for catheter-associated coagulase-negative staphylococcal infection. We will determine whether lipids facilitate adherence of coagulase-negative staphylococci to intravascular catheters and increase catheter associated bacteremia, either by enhancing colonization of catheters by organisms or by lowering host resistance to infection. The immunologic studies will extend our observations in rabbits that immunization with PS/A protects against bacteremia due to coagulase-negative staphylococci. We will explore whether monoclonal antibodies PS/A, derived from the same parental hybridoma but with different heavy chains (i.e isotype switched), differ in their ability to mediate in vitro opsonic killing of coagulase-negative staphylococci and prevent adherence to catheter materials. These antibodies will then be tested for the ability to passively protect rabbits against in vivo colonization of catheters and bloodstream dissemination from an infected catheter. Finally we will extend studies on the human immune response to PS/A to try and document whether quantitative or functional defects in antibody to PS/A are found in patients with coagulase-negative staphylococcal bacteremias. By the end of the next funding period, we expect to have a clear understanding of the biochemistry and immunology of PS/A antigen, a definition of its role in pathogenesis of coagulase-negative staphylococcal infection, and the potential to develop immunotherapies to prevent infection in patients at-risk for this disease.
Showing the most recent 10 out of 12 publications
