Post by Rebecca Way, University of Aberdeen
Silver nanoparticles have been shown to have effective antibacterial activity against a range of disease-causing bacteria. In this study featured in the Journal of Medical Microbiology, nano-silver was put to the test against human pathogenic bacterial strains including; Escherichia coli, Staphylococcus aureus and Pseudomonas aeruginosa. To explore and evaluate the potential antibacterial properties of silver particles, experiments were carried out comparing the effects of nano-silver alone and in combination with traditionally used antibiotics including ampicillin and kanamycin.
Results showed high inhibition of bacteria using nano-silver particles alone. All combinations of nano-silver with various antibiotics showed antibacterial activity. Silver was used in medicine for its antimicrobial properties as early as the 19th century and more recently has been used in wound dressings and catheters. Nano-silver is less reactive than silver ions, making it more suited to medical applications. Nano-silver has been shown to induce programmed cell death. The current challenge is to measure this activity, understand it at the molecular level and then determine effective concentrations for use in therapy.
As frequently reported, bacteria are becoming more resistant to antibiotics, leading to outbreaks of superbugs like methicillin-resistant Staphylcoccus aureus in hospitals and communities. There is a lack of new antibiotics being licensed for use and so alternative therapies are being researched for their antibacterial properties. One property that makes it difficult for antibiotics to target bacteria is the formation of bacterial biofilms. A biofilm is a complex microbial community that grows on a solid, moist substrate and is surrounded by a three-dimensional gel matrix – protecting bacterial cells. In this study, results indicated that nano-silver particles alone inhibit biofilm growth by less than 40%. However, in combination with antibiotics like kanamycin, anti-biofilm activity was significantly greater. This is encouraging, as it could mean lower doses of antibiotics are needed, when combined with silver, in treating patients.
Another advantage of nano-silver is its ability to induce hydroxyl radicals (also produced by some antibiotics) to kill bacterial cells. Interestingly, higher quantities of hydroxyl radicals were produced when nano-silver was combined with non-radical-producing antibiotics. Importantly, nano-silver was not found to interact with the multidrug-resistant pumps in bacteria which release toxins attacking antibiotics like ampicillin. This suggests that resistance to nano-silver particles would be unlikely to occur.
The study demonstrates the synergistic activity of silver nanoparticles in combination with other compounds, showing that antibacterial agents can be more powerful in combination, than the sum of their individual effects. This highlights the advantages of using nano-silver as an adjuvant in treating infections. It is important to continually address the issue of increasing antibiotic resistance and find new ways of treating these infections successfully. Nano-silver is non-toxic and a safe antibacterial agent; developments for patient use are currently underway, which present an exciting horizon in the future of antibiotics.