LEUKOCYTE-BIOMATERIAL INTERACTIONS IN THE PRESENCE OF STAPHYLOCOCCUS-EPIDERMIDIS - FLOW CYTOMETRIC EVALUATION OF LEUKOCYTE ACTIVATION

The adhesion of bacteria on a biomaterial surface is believed to be th e first step in the development of biomaterial-related infection. The goal of this study was to investigate the mechanisms that permit adher ent bacteria to persist on the surface of an implanted cardiovascular biomaterial. We hypothesized that circulating leukocytes are unable to adhere to the biomaterial surface under physiologic shear stress cond itions, and this prevents them from interacting with adherent bacteria . To address this hypothesis, we investigated the adhesion profiles of Staphylococcus epidermidis and polymorphonuclear leukocytes (PMN), in cubated under controlled shear stress conditions with the test biomate rial. We found that bacteria could adhere on the biomaterial surface, even when their concentration in the test medium was as low as 10(3) c fu/mL. At this concentration, the bacteria did not induce significant complement activation. PMN adhesion on the biomaterial surface was sen sitive to shear stress and minimal at shear stress >10 dynes/cm(2). Lo w concentrations of bacteria could induce a significant increase in th e expression of PMN adhesion molecules CD11b and CD11c. We conclude th at the presence of bacteria induces PMN activation but does not increa se PMN adhesion on biomaterial surfaces under physiologic shear stress conditions. This could be a major mechanism that protects adherent ba cteria from PMN antibacterial activity. (C) 1997 John Wiley & Sons, In c.