Bioactive glass S53P4 eradicates Staphylococcus aureus in biofilm/planktonic states in vitro

Abstract

Background: Increasing antimicrobial resistance to antibiotics is a substantial health threat. Bioactive glass S53P4 (BAG) has an antimicrobial effect that can reduce the use of antibiotics. The aim of this study was to evaluate the antimicrobial efficacy of BAG in vitro on staphylococci in biofilm and in planktonic form. Secondary aims were to investigate whether supernatant fluid primed from BAG retains the antibacterial capacity and if ciprofloxacin enhances the effect.

Methods: BAG-S53P4 granules, <45 µm, primed in tryptic soy broth (TSB) were investigated with granules present in TSB (100 mg/mL) and after removal of granules (100, 200, and 400 mg/mL). The efficacy of BAG to eradicate Staphylococcus aureus biofilm in vitro was tested using 10 different clinical strains and 1 reference strain in three test systems: the biofilm-oriented antiseptic test based on metabolic activity, the biofilm bactericidal test based on culturing surviving bacteria, and confocal laser scanning microscopy (CLSM) combined with LIVE/DEAD staining.

Results: Exposure to 48 h primed BAG granules (100 mg/mL) produced bactericidal effects in 11/11 strains (p = 0.001), and CLSM showed reduction of viable bacteria in biofilm (p = 0.001). Supernatant primed 14 days, 400 mg/mL, reduced metabolic activity (p < 0.001), showed bactericidal effects for 11/11 strains (p = 0.001), and CLSM showed fewer viable bacteria (p = 0.001). The supernatant primed for 48 h, or in concentrations lower than 400 mg/mL at 14 days, did not completely eradicate biofilm.

Conclusion: Direct exposure to BAG granules, or primed supernatant fluid, effectively eradicated S. aureus in biofilm. The anti-biofilm effect is time- and concentration-dependent. When BAG had reached its full antimicrobial effect, ciprofloxacin had no additional effect.

Keywords:

• BAG
• biofilm
• confocal laser scanning microscopy
• Staphylococcus aureus

Acknowledgements

The authors thank the staff at the Department of Microbiology at the Oslo University Hospital and the Norwegian Veterinary Institute for their excellent support that allowed us to perform the sample analysis in this paper.

Disclosure statement

The authors have no conflict of interest in the subject matter or materials discussed in this manuscript.

Author contributions

TG and JTS conceived the study; TG, LKV, LLN, MvU, and JTS conducted research and analysed data; TG wrote the first draft and reviewed it with JTS. All authors contributed to, read, and approved the manuscript.

Additional information

Funding

The project was funded by the University of Oslo.

Notes on contributors

Torstein Grønseth

Torstein Grønseth is a consultant at the Department of Otolaryngology, Head and Neck Surgery, Oslo University Hospital, Oslo, Norway and a research fellow at the Institute for Clinical Medicine, University of Oslo, Oslo, Norway.

Lene K. Vestby

Lene K. Vestby is Head of Section for immunology and virology, Department of Analysis and Diagnostics at the Norwegian Veterinary Institute. She is also a senior researcher and hold a PhD in bacteriology.

Live L. Nesse

Live L. Nesse, DVM, PhD, Dr.med.vet, is a senior research scientist at the Norwegian Veterinary Institute.

Magnus von Unge

Magnus von Unge, MD, PhD, is a ear surgeon and a professor emeritus at the Department of Clinical Medicine, University of Oslo, Norway.

Juha T. Silvola

Juha T. Silvola is a senior consultant in Otology-otoneurology and Audiology in Akershus university hospital (Ahus) and Head for the Research department in the Surgical division of Ahus. In addition, he is an associate professor at the Institute of Clinical Medicine, Campus Ahus, University of Oslo, Norway.