Potassium iodide potentiated photodynamic inactivation of enterococcus faecalis using toluidine blue: comparative analysis, photothermal effect, and post - treatment biofilm formation study

Abstract

Antimicrobial Photodynamic Inactivation (aPDI) has recently gained interest as an alternative modality to fight pathogenic entities. Its effect can also be further enhanced by using certain inorganic salts. Here, the Potassium Iodide (KI) - mediated aPDI effect on Enterococcus faecalis using Toluidine Blue Ortho (TBO) as photosensitizer (PS) has been evaluated, and the Photothermal effect as well as subsequent Biofilm formation extent are accounted for. The comparative photoinactivation of TBO and TBO/KI on E.faecalis was investigated by quantifying surviving bacterial colonies after laser irradiation with 30,60,and 180 second exposure times and different PS/Potentiator concentrations. The degree of photothermal effect was measured by obtaining a temperature profile using thermocouple. The biofilm formation capability of E.faecalis was observed by calculating Optical Density (OD595) of samples 0, 24, 48, and 72 hours post- aPDI treatment. Scanning Electron Microscopy (SEM) was used as a qualitative measure of bacterial biofilm growth. More than 4 LOGS of photokilling was obtained for experimental groups with the highest PS/KI concentrations at 180 s exposure time. All KI-potentiated groups showed enhancement in aPDI effect when compared to non-potentiated counterparts. Moreover, an average temperature increase of about 2°C,with 180 s laser exposure, proved photothermal effect to be negligible. The degree of recurring biofilm for laser-treated groups also showed to be much less than that of control group, as confirmed by both OD595 measurement and SEM imaging.|Keywords : E.faecalis, TBO, aPDI, Biofilm, Potassium Iodide, Potentiator.