EVALUATING THE INTERACTION OF BACTERIA WITH BIOMATERIALS USING ATOMIC-FORCE MICROSCOPY

Bacterial infection of biomaterials represents one of the most importa nt reasons for the failure of transdermal or implanted medical devices . The first and least understood step in biomaterial-associated infect ions is the initial interaction between bacteria and a surface. This i nitial interaction can be either attractive or repulsive depending on the physiochemical nature of the biological and synthetic surfaces, as well as the properties of the interstitial fluid. We have shown that atomic force microscopy (AFM) can be employed as an exquisitely sensit ive and versatile tool for quantifying the interaction between bacteri a and surfaces in physiological solutions. The forces of interaction b etween an AFM cantilever tip and a uniform lawn of bacteria immobilize d on glass were determined. By comparing the interactions of cantileve r tips with lawns of isogenic E. coli strains carrying genetic lesions that alter their cell surface composition, it was possible to evaluat e the effect of macromolecules such as lipopolysaccharide and capsular polysaccharide on the adhesion process. Mutations that result in the synthesis of truncated lipopolysaccharide or in the overproduction of the negatively charged capsular polysaccharide colanic acid render the interaction of the bacteria. with the AFM tip unfavorable due to incr eased electrostatic repulsion. Furthermore, AFM could be used to evalu ate the adhesion of bacteria. onto commercially relevant biomaterials. In one approach, micron-size polystyrene beads were attached to AFM t ips which Mere then used to measure forces. Unfortunately, this approa ch is limited by the meager number of materials manufactured as bead, of a size suitable for AFM measurements. As an alternative approach, A FM cantilever tips were coated with a confluent layer of bacteria and used to probe planar surfaces. In this configuration, AFM could be emp loyed to measure the force of interaction between virtually any bacter ium and surface of interest.