UBC Theses and Dissertations
Dynamics of killing biofilm bateria Stojicic, Sonja
Oral bacteria are the main cause of common oral diseases such as caries, periodontal infection and root canal infections. Bacteria in nature survive predominantly as biofilms, which are complex microbial communities composed of populations of microorganisms adhered to living or non-living surfaces and embedded in a self-produced matrix of extracellular polymeric substance (EPS). Various biofilm models have been developed to simulate the real situation in nature. In this thesis, I studied a new in vitro biofilm model, and examined the antimicrobial efficacy of current as well as newly developed endodontic irrigants/protocols against planktonic and biofilm bacteria. Single and multispecies biofilms were grown on sterile hydroxyapatite and dentin discs coated with bovine dermal collagen Type I . Transmission electron microscopy (TEM) was used to examine the biofilm microorganisms. The antimicrobial effect of sodium hypochlorite (NaOCl), iodine potassium iodide (IPI), chlorhexidine (CHX) and a new disinfecting agent (QMiX- a mixture of CHX, EDTA, and a detergent) was evaluated. The antimicrobial strategies included in the studies were photoactivated disinfection (PAD) and its experimental modifications. Biofilms at different stages of maturation were exposed to various antibacterial agents, and the killing of biofilm bacteria was observed using viability staining and confocal laser scanning microscopy (CLSM). The new in vitro biofilm model had similarities to in vivo biofilms, as described in the literature. This biofilm model reached maturation between two and three weeks. Mature biofilms were less sensitive to disinfecting agents than young biofilms. The time required for the biofilms to become resistant to disinfecting agents (maturation) was not dependent on the source of biofilm bacteria or the type of disinfectant used. Modified photoactivated disinfection was up to almost twenty two times more effective in killing biofilm bacteria than conventional PAD and up to almost eight times more effective than the commonly used endodontic irrigants. A new endodontic irrigant, QMiX was more effective in killing planktonic and biofilm bacteria than 2% CHX, BioPure MTAD (a mixture of tetracycline isomer, an acid, and a detergent), and 1% and 2% NaOCl.The new biofilm model seems promising for testing and developing efficient methods to eradicate oral biofilm bacteria.
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