Effect of Antibacterial Phosphate Based Glasses on Oral Biofilm Models

Objectives: To evaluate the efficacy of antibacterial phosphate based glasses (PBGs) on dual species biofilm models of Porphyromonas gingivalis ATCC 33227 (Pg) and Streptococcus gordonii DL1 (Sg). Methods: PBG rods of (CaO)_x(Na₂O)_47-x(P₂O₅)₄₅(Ga₂O₃)₃(Ag₂O)₅, where x = 10, 11 and 12 (given the abbreviations C10, C11 and C12 respectively), and a control with no gallium and silver (C) were prepared using a conventional melt quenching method, at 1100⁰C for 1 hour. Dual species biofilms of Pg and Sg were grown on nitrocellulose membrane filters (NMF) laid atop fastidious anaerobic agar (FAA) plates. The glass discs were placed in the centre of the NMF and incubated anaerobically at 37⁰C for 72h. The plates were then assessed for viable colony forming units (CFUs) of bacteria on FAA plates. A second set of biofilm experiments were performed on hydroxyapatite, C10 and C glass samples in a constant-depth film fermentor (CDFF) operated under anaerobic conditions. The CFUs in the biofilms were enumerated on FAA plates in triplicates. Results: All PBGs showed statistically significant (p£0.0115) growth inhibition of Sg (C10; 10.34±0.29, C11; 10.54±0.22, C12; 10.82±0.03 and C; 11.22±0.15) on NMF biofilm model whereas only C10 (C10; 10.0±0.15 and C; 10.65±0.2) PBGs achieved a statistically significant growth inhibition of Pg (p£0.011) compared with the control. In the CDFF biofilm model, Pg alone maintained statistically significant reduction (p£0.005) in CFUs compared with controls (with a maximum of 1.92 log₁₀CFU reduction after 168 h). Conclusions: The antibacterial PBGs displayed biofilm growth inhibitory action against the putative periodontal pathogen Pg in two dual species laboratory biofilm models along with a common early coloniser of dental plaque, Sg. The results indicate the potential use of PBGs as a therapeutic agent in the treatment of oral diseases.