Synergistic Activity of Silver Nanoparticles and Vancomycin Against a Spectrum ofStaphylococcus aureusBiofilm Types

Staphylococcus aureus (SA) is an important human pathogen, causing potentially lethal infections of the blood, skin, and lungs. SA is becoming increasingly difficult to treat due to high levels of antibiotic resistance, and new treatments are needed. SA is able to evade antibiotics and immune surveillance through biofilm development. Biofilms are communities of microorganisms that are able to prevent the entry of antimicrobials and immune cells. Biofilms are also involved in SA transmission because biofilms can form on medical devices. In this study, we tested silver nanoparticles and vancomycin for their anti-biofilm effects on SA. We used 10 different SA isolates, representing a spectrum of biofilm-forming ability, and a crystal violet assay to measure biofilm mass. 2μg/mL vancomycin treatment resulted in a significant reduction in established SA biofilms in 7/10 isolates, including 4/5 methicillin susceptible SA (MSSA) and 3/5 methicillin-resistant (MRSA) isolates (mean reduction in crystal violet stain of 13.0%; high of 26.5% and low of 0%). Silver nanoparticle treatment of SA biofilms resulted in a significant reduction in 6/10 isolates, including 4/5 MSSA and 2/5 MRSA (mean reduction of 8.7%; high of 21.2% and low of 0%). A combinatorial treatment with silver nanoparticles and vancomycin resulted in significant reductions in 9/10 isolates (mean reduction of 20.8%; high of 39.3% and low of 0%). We conclude that both vancomycin and silver nanoparticle treatment of established tissue culture-based SA biofilms result in significant reductions in biofilm mass, with a combinatorial treatment even more effective than either treatment alone.