The antibacterial effect of silver with different release kinetics

Sammanfattning: Hard to heal wounds are painful and the patient has to stand with them for a long time, also these wounds are an economical burden for health care systems. One important factor that may interrupt the healing of wounds is contamination bacterial and they can also cause infections. Today, there are numerous of silver releasing dressings on the market that have effect against a wide range of bacterial over multiple days. The available silver dressings contain different amounts of silver and have different release kinetics.

The aim with this Master thesis is to find out how the release profile of silver influences the antibacterial effect, and if one silver release profile is more preferable to another and if it is valid for bacterial both in logarithmically and stationary growth phase.

Two wound pathogens, Staphylococcus aureus and Pseudomonas aeruginosa, in either log- (~10⁶ CFU/mL) or stationary- growth phase (10⁸-10⁹ CFU/mL) were cultured in simulated wound fluid. Silver sulfate solutions were added to the bacterial suspension, the suspensions were incubated for 24 h and viable count were determined by plate counts method. For log-phase bacteria, the Minimum Inhibitory Concentration (MIC)and Minimum Bactericidal Concentration (MBC) were 8 ppm and 32 ppm for S.aureus and 6.5 ppm and about 7 ppm of silver for P. aeruginosa, respectively. For stationary-phase bacteria MBC's were found to be above 987 ppm and above 65 ppm of silver for S. aureus and P. aeruginosa, respectively. The MIC and MBC values were determined to find appropriate silver concentrations to simulate silver release profiles. it was also found that vortex of the bacterial suspensions after addition of silver increased the antibacterial effect significantly.

Three silver release profiles (corresponding MIC, boost, linear) were simulated by adding different amounts of silver every second hour (0, 2, 4 and 6 h)for six hours and then incubated further for 24 h in total. There was no significant antibacterial difference between the three release profiles when S. aureus was exposed. In contrast, the linear release profile for P. aeruginosa in log- and stationary-phase had 3 and 3.5 log reductions less antibacterial effect, respectively, compared to the profile corresponding to MIC measurements.