Citrate-Capped Silver Nanoparticles Showing Good Bactericidal Effect against Both Planktonic and Sessile Bacteria and a Low Cytotoxicity to Osteoblastic Cells

Abstract

A common problem with implants is that bacteria can form biofilms on their surfaces, which can lead to infection and, eventually, to implant rejection. An interesting strategy to inhibit bacterial colonization is the immobilization of silver (Ag) species on the surface of the devices. The aim of this paper is to investigate the action of citrate-capped silver nanoparticles (AgNPs) on clinically relevant Gram-positive (Staphylococcus aureus) and Gram-negative (Pseudomonas aeruginosa) bacteria in two different situations: (i) dispersed AgNPs (to assess the effect of AgNPs against planktonic bacteria) and (ii) adsorbed AgNPs on titanium (Ti) substrates, a material widely used for implants (to test their effect against sessile bacteria). In both cases, the number of surviving cells was quantified. The small amount of Ag on the surface of Ti has an antimicrobial effect similar to that of pure Ag surfaces. We have also investigated the capability of AgNPs to kill planktonic bacteria and their cytotoxic effect on UMR-106 osteoblastic cells. The minimum bactericidal concentration found for both strains is much lower than the AgNP concentration that leads to cytotoxicity to osteoblasts. Planktonic P. aeruginosa show a higher susceptibility to Ag than S. aureus, which can be caused by the different wall structures, while for sessile bacteria, similar results are obtained for both strains. This can be explained by the presence of extracellular polymeric substances in the early stages of P. aeruginosa biofilm formation. Our findings can be important to improving the performance of Ti-based implants because a good bactericidal action is obtained with very small quantities of Ag, which are not detrimental to the cells involved in the osseointegration process.

Hierarchical micro/nanostructured titanium with balanced actions to bacterial and mammalian cells for dental implants

“…Previous studies have shown that diffusive Ag NPs could be readily taken up by mammalian cells through endocytosis and macropinocytosis and release of Ag + directly damages intracellular functions. 18 In this study, the amount of released Ag + is negligible, and the Ag NPs immobilized using Ag-PIII technique showed almost no side effects to rBMSCs in terms of initial adhesion, cell proliferation, and osteoblastic differentiation. It appeared that Ag + is safe and cytocompatible at low concentrations, although high concentrations of Ag + might induce cytotoxicity.…”

“…52 In fact, it was reported that Ag NPs could reduce the mitochondrial functions and also affect the membrane integrity of mammalian cells. 18 In addition, Ag NPs were identified as responsible for the production of reactive oxygen species and interruption of adenosine triphosphate synthesis, which, in turn, cause DNA damage. 18 Thus, given its potential cytotoxicity, we have tested the cytocompatibility of Ag-PIII groups with rBMSCs, the most well-characterized cell source involved in osseointegration.…”

“…17 Thus, an effective strategy to inhibit bacterial colonization is the local administration of an antibacterial agent on implant surfaces, which can inhibit adhesion of pioneer bacteria and kill them when they try to attach to the surface. 18,19 Silver as a nonspecific biocidal agent is able to act strongly against a broad spectrum of bacterial and fungal species, including antibiotic-resistant strains. 20 Silver nanoparticles (Ag NPs) are believed to be more reactive than the bulk metallic forms due to the larger active surface area.…”

“…39 Although the cell wall of some bacteria remains intact after being exposed to the Ag NPs-incorporated surfaces, the number of bacteria capable of replicating and hence able to form a biofilm was only a fraction of the live bacterial population. 18,50 In contrast to the Live/Dead assay, the spread plate methods reveal only viable bacteria, which was more precise and reliable.…”

Minimum bactericidal concentration of chemically synthesized silver nanoparticles against pathogenic Salmonella and Shigella strains isolated from layer poultry farms

“…Moreover, the efficient bactericidal activity of AgNPs was obtained at its lowest concentration of 0.35 μgml -1 (Devi et al, 2017). Furthermore, the MBC value of 100 nm sized AgNPs was ≈1 × 104 μgml -1 , while that for 5-10 nm sized AgNPs was 12-25 μgml -1 (Flores et al, 2013). A previous study reported that the calculated MIC of 28 nm sized AgNPs against Salmonella was 25 μgml -1 while it was 12.5 μgml -1 in case of 8 nm sized AgNP (Smekalova et al, 2016).…”