Please use this identifier to cite or link to this item: http://scholarbank.nus.edu.sg/handle/10635/18016
Title: Influence of Bacterial Growth Modes on the Susceptibility to Light Activated Disinfection
Authors: MEGHA HARIDAS UPADYA
Keywords: Light Activated Disinfection, Antimicrobial Photodynamic Therapy, Photosensitizer, Methylene blue, Eneterococcus faecalis, Biofilm
Issue Date: 13-Jan-2010
Source: MEGHA HARIDAS UPADYA (2010-01-13). Influence of Bacterial Growth Modes on the Susceptibility to Light Activated Disinfection. ScholarBank@NUS Repository.
Abstract: Studies in literature have emphasized the importance of bacterial aggregates, co-aggregates and biofilms in root canal infections. The harsh environmental conditions prevailing in the root canal may favor the growth of bacteria as a biofilm since this mode of growth represents an important survival strategy. In this context it is crucial to understand the growth of bacteria in different modes and elucidate the influence of these growth modes on the survival of bacteria when faced with an antimicrobial challenge. Recently, Light Activated Disinfection (LAD) has emerged as a possible supplement to the existing protocols for root canal disinfection. So far, many studies have demonstrated the LAD-mediated inactivation of various species of bacteria but few have correlated the efficacy of LAD to inactivate bacteria in different growth modes. In the first phase of this study, experiments were conducted to evaluate and compare the ability of cationic photosensitizers (PS) such as methylene blue (MB) and toluidine blue (TBO) vs. anionic PS such as rose bengal (RB) in the LAD-mediated inactivation of Enterococcus faecalis. Subsequent experiments, evaluated the influence of different bacterial growth modes (planktonic, co-aggregation, biofilms) on the susceptibility of gram-positive E. faecalis and gram-negative Pseudomonas aeruginosa to LAD. Furthermore, the use of an efflux pump inhibitor (EPI) in potentiating the anti-biofilm efficacy of E. faecalis in combination with LAD and varying concentrations of aqueous calcium hydroxide was also evaluated. In the second phase of the study, LAD experiments on E. faecalis and P. aeruginosa biofilms using modified PS formulations such as: (a) a mixture of glycerol:ethanol:water (30:20:50) (MIX) (b) an emulsion of perfluorodecahydronapthalene:H2O2:triton-X100 (75:24.5:0.5) were conducted. The efficacy of these formulations was further tested in an in vitro bio-molecular biofilm model. The findings from this study showedthat LAD using cationic PS such as MB and TBO were more effective against E. faecalis when compared to the anionic PS RB (p<0.05). Among the three bacterial growth modes evaluated, the biofilm mode of growth was significantly resistant to MB-mediated LAD when compared to the same in suspension (p<0.001). The anti-biofilm efficacy of LAD with the MB¿EPI combination on E. faecalis was significantly potentiated when compared to LAD with MB alone (p<0.001). However, the effect of the EPI with calcium hydroxide was significant only when used with lower concentrations (p<0.001). Among the different MB formulations tested for LAD, the order of effectiveness in inactivating and disrupting E. faecalis and P. aeruginosa biofilms was of the order: MIX + emulsion > MIX > water (p<0.001). When LAD using these formulations was tested in an in vitro bio-molecular biofilm model, there was complete inactivation of the resident bacteria and significant disruption of the biofilm structure with the use of MB in a MIX formulation followed by an MB-based emulsion during irradiation (p<0.001). In summary, this study showed that bacterial growth modes differentially affected the susceptibility of the tested bacterial species to LAD. Biofilm mode of growth was found to offer the greatest resistance to LAD and the use of EPIs and modified MB formulations could significantly potentiate the anti-biofilm efficacy of LAD.
URI: http://scholarbank.nus.edu.sg/handle/10635/18016
Appears in Collections:Master's Theses (Open)

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