Dosimetry of pulsed magnetic field towards attaining bacteriostatic effect on Enterococcus faecalis: Implications for endodontic therapy.

Abstract

To examine in a laboratory setting the efficacy of moderate to high strength magnetic fields, as a potential bacteriostatic stimulus, against Enterococcus faecalis, one of the causative agents for infection during root canal treatments. Four different strengths (1, 2, 3 and 4T) of the pulsed magnetic field (PMF) were applied in thirty repetitions to bacterial suspension. A pickup coil setup was used to measure the electromotive force induced inside the bacterial suspensions. The optical density (OD) was monitored over time (for 16h 40min) during the post-treatment period to assess bacterial growth. Along with the change in OD values, live/dead assay, membrane depolarization study, atomic force microscopy (AFM), scanning electron microscopy (SEM) and reactive oxygen species (ROS) assay on selected samples were studied to evaluate the effect of PMFs. All results were analysed using one-way ANOVA followed by post hoc Tukey test and considered significant at p<.05. Regression analysis (at a confidence of 95%, α=0.05) was performed on the bacterial growth and membrane depolarization studies to determine progressive changes of the outcomes. The peak value of the induced electromotive force was recorded as 0.25V, for the 4T magnetic field pulse with a pulse width of 16ms. There was a significant arrest of bacterial cell growth after an exposure to PMFs of 1T, 3T and 4T (ANOVA score: F (4, 495) =395.180 at p=.05). The image-based qualitative results of the live/dead assay using fluorescence microscopy techniques indicated that an exposure to higher PMFs (3T/ 4T) induced a bacteriostatic effect in a longer post-exposure timescale. Evidence of altered membrane potential within the 2h of exposure to 4T PMF was supported by the incidence of elevated ROS. For the ROS assay, a significant difference occurred for 4T exposed samples (ANOVA score: calculated F (1, 3) =20.2749 at p=.05). SEM and AFM observations corroborated with the outcomes, by portraying significant membrane damage. In a laboratory setting, PMFs with higher magnitudes (3T and 4T) were capable of inducing bacteriostatic effects on E.faecalis.