Positively charged biomaterials exert antimicrobial effects on gram-negative bacilli in rats

Biomaterial-centered infection is a much-dreaded complication associated with the use of biomedical implants. Although positively charged biomaterial surfaces stimulate bacterial adhesion, it has been suggested that surface growth of adhering Gram-negative bacilli is inhibited on positively charged surfaces. In the present paper, we determined the infection rate of differently charged poly(methacrylates) in rats. To this end, 2 x 10(6)/cm(2) Escherichia coli O2K2 or 2 x 10(4)/cm(2) Pseudomonas aeruginosa AK1 were seeded on glass discs coated with three differently charged poly(methacrylates) coatings in a parallel plate flow chamber. Three rats received six subcutaneous discs (two discs of each charge variant) seeded with E. coli, while three other rats received discs seeded with P. aeruginosa. The numbers of viable bacteria on the surfaces were determined 48h after implantation. On 50% of all positively charged discs viable E. coli were absent, while the negatively charged discs were all colonized by E. coli. P. aeruginosa, however, were isolated from both positively and negatively charged discs. Probably, P. aeruginosa can circumvent the antimicrobial effect of the positive charge through the formation of extracellular polysaccharides.