Efficacy of silk fibroin-nano silver against Staphylococcus aureus biofilms in a rabbit model of sinusitis

Abstract

Background: Staphylococcus aureus biofilms contribute significantly to the recalcitrant nature of chronic rhinosinusitis. In previous studies, it has been shown that silk fibroin-nano silver solution can eliminate S. aureus biofilms in vitro, which suggests a potential role of this novel agent in the treatment of biofilm-associated diseases, such as sinusitis.

Objective: The aim of this study was to investigate the efficacy of silk fibroin-nano silver solution as a topical anti-biofilm agent in a rabbit model of sinusitis.

Methods: Biofilm-associated sinusitis models were established in 24 New Zealand White rabbits by gelatin sponge placement and S. aureus inoculation through a hole drilled into the anterolateral wall of the right maxillary sinus. After 4 weeks, indwelling catheters were placed into the maxillary sinus. Different concentrations of silk fibroin-nano silver solution or normal saline were irrigated slowly into the maxillary sinus via the indwelling catheters. After 7 days of irrigation, the rabbits were sacrificed. The sinus mucosa was harvested and examined for biofilm biomass as well as morphological integrity of the epithelium by scanning electron microscopy.

Results: Silk fibroin-nano silver solution was found to be most effective in reducing the biomass of the S. aureus biofilms at a concentration of 384 mg/L, followed by the concentration of 153.6 mg/L, when compared with saline. After treatment with 384 mg/L silk fibroin-nano silver solution, the biofilms were completely eliminated and the injured epithelium was almost restored with regenerated cilia on the surface.

Conclusion: Silk fibroin-nano silver solution was found to be an effective topical agent against S. aureus biofilms in the rabbit model of sinusitis, and its effect was concentration-dependent.

Keywords: animal; biomass; chronic rhinosinusitis; maxillary sinus; nasal irrigation; scanning electron microscopy.

Figure 1

Synthesis mechanism and characterization of SF-NS composite. Notes: (A) Possible mechanism of the reduction of Ag⁺ ion by tyrosine residues in silk fibroin chain. (B) Transmission electron microscopy images of the synthesized SF-NS particles. (C) High-resolution transmission electron microscopy image of an individual nanoparticle and the electron diffraction pattern. (D) Energy dispersive X-ray spectrum at a single nanocrystal level of the synthesized SF-NS composite. Abbreviation: SF-NS, silk fibroin–nano silver.

Figure 2

Methodology for implantation of indwelling catheter and sinus irrigation. Notes: (A) A plastic catheter connected with an end-enlarged stainless steel needle (arrow) is being tunneled under the dorsum. (B) The catheter is secured in place by fixation of the enlarged needle end under the skin (*). (C) The plastic end is inserted in the right maxillary sinus. (D) Topical nasal irrigation method. Abbreviation: SF-NS, silk fibroin–nano silver.

Figure 3

Representative scanning electron microscopy images of sinus mucosa from each group. Notes: (A) Animal model without nasal irrigation. (B–D) Animal models after 7 days of nasal irrigation with (B) normal saline, (C) SF-NS solution (153.6 mg/L), and (D) SF-NS solution (384 mg/L) (A1–D1, 2,000×; A2–D2, 5,000×). Abbreviation: SF-NS, silk fibroin–nano silver.