Enhanced bactericidal toxicity of silver nanoparticles by the antibiotic gentamicin†
The alteration of properties of nanomaterials in the environment may change the interaction of the nano–bio interface and the corresponding bio-responses. In this study, we find that the antibiotic gentamicin significantly enhances the antibacterial activities of poly(N-vinyl-2-pyrrolidone) coated silver nanoparticles (Ag-PVP NPs) by altering the properties of silver nanoparticles in culture media. The enhanced antibacterial activities of Ag-PVP NPs against three bacterial strains (S. aureus, E. coli and gentamicin-resistant E. coli) are concluded according to the data of the fractional inhibitory concentration indices, bacterial survival rates and growth curves. A thorough investigation indicates that gentamicin promotes the dissolution of Ag-PVP NPs dramatically, which not only increases the concentration of silver ions in the system but also facilitates the attachment of Ag-PVP NPs onto the surface of bacteria by mitigating the negative charge of the NPs. The corresponding sequence is the augmented bacterial growth inhibition and death. Meanwhile, it is surprisingly found that gentamicin also binds with the dissolved silver ions and then inhibits the antibacterial activity of silver ions. In other words, gentamicin plays a dual role in the antibacterial activity of Ag-PVP NPs. This study is valuable for understanding the bioeffects of nanoparticles in a complex system.