Antimicrobial effects of positively charged surfaces on adhering Gram-positive and Gram-negative bacteria

The infection of biomaterials is determined by an interplay of adhesion and surface growth of the infecting organisms. In this study, the antimicrobia l effects on adhering bacteria of a positively charged poly(methacrylate) s urface ( potential +12 mV) were compared with those of negatively charged p oly(methyl methacrylate) (-12 mV) and a highly negatively charged poly(meth acrylate) (-18 mV) surface. Initial adhesion of Staphylococcus aureus ATCC 12600, Staphylococcus epidermidis HBH2 102, Escherichia coli O2K2 and Pseud omonas aeruginosa AK1 to these surfaces was measured in a parallel plate fl ow chamber in phosphate-buffered saline. Adhering bacteria were allowed to multiply by perfusing the flow chamber with growth medium. All bacteria adh ered most rapidly to the positively charged surface, but there was no subse quent surface growth of the Gram-negative strains. On the negatively charge d surfaces, despite a slower initial adhesion, surface growth of the adheri ng bacteria was exponential for both Gram-positive and Gram-negative strain s. These results suggest that positively charged biomaterial surfaces exert an antimicrobial effect on adhering Gram-negative bacteria, but not on Gra m-positive ones.