Ales Panacek

Abstract:

Silver nanoparticles (NPs) exhibit significant antimicrobial activity against a broad range of bacteria and fungi at concentrations ranging from a few ppm to tens of ppm that are not cytotoxic to human cells [1,2]. Silver NPs also strongly enhance antibacterial activity against multiresistant, beta-lactamase and carbapenemase-producing Enterobacteriaceae when combined with antibiotics such as cefotaxime, ceftazidime, meropenem, ciprofloxacin and gentamicin [3]. All the antibiotics, when combined with silver NPs, showed enhanced antibacterial activity at concentrations far below the minimum inhibitory concentrations (tenths to hundredths of one ppm) of individual antibiotics and silver NPs. As a result, silver NPs have already been successfully applied in various biomedical and antimicrobial technologies and products used in every-day life as an alternative to conventional antimicrobials. While bacterial resistance to antibiotics has been discussed extensively in the literature, the possible development of resistance to silver NPs after repeated long-term exposure has not been fully explored. We report that the Gram-negative bacteria can develop resistance to silver NPs after prolonged exposure. The observed resistance stems from the production of the adhesive flagellum protein flagellin, which triggers the aggregation of silver NPs and eliminates their antibacterial effects. The resistance mechanism cannot be overcome by stabilization of silver NPs, by polymers or by surfactants. It is possible, however, to suppress it by inhibiting flagellin production with pomegranate rind extract [4].

[1] Panacek A., Kvitek L., Prucek R. et al., J. Phys. Chem. B 110, 33 (2006) 16248-16253.
[2] Panacek A., Kolar M., Vecerova R. et al., Biomaterials 30, 31 (2009) 6333-6340.
[3] Panacek A., Smekalova M., Vecerova R., et al., Colloids Surf., B 142 (2016) 392-399.
[4] Panacek A., Kvitek L., Smekalova M. et al., Nature Nat. 13, (2018) 65-72.