Synergistic potential of antibiotics against an in vitro multispecies biofilm model for peri-implantitis

Background: and to assess the influence of implant material on their efficacy. Method: An oral multispecies biofilm model (MSBM) was cultivated in the presence of the antibiotics amoxicillin (Amox), doxycycline (Doxy), minocycline (Mino), and metronidazole (Metro), both as single agents and in combination with Metro at varying concentrations. Synergistic effects were assessed by turbidity measurement, Bactiter Glo™ assay and Resazurin assay. The most effective concentrations were further examined using confocal laser scanning microscopy. Additionally, they were tested on three potential implant materials: titanium grade 4, titanium grade 5, and an experimental ultrafine-grained niobium alloy and on a mature biofilm. Results: Amox, Doxy and Mino demonstrated strong efficacy against the MB, whereas Metro alone showed little to no effect. Synergistic interactions were mainly observed when comparing to Metro's limited activity. A tendency toward enhanced efficacy of Amox and Doxy in combination with Metro was noted, although not statistically significant. The antibacterial performance of all agents was independent of the implant material and reduced when applied on mature biofilm. Conclusion: biofilms are warranted to optimize antibiotic combinations and concentrations for clinical application.