Escherichia coli Sterilization Using a Light-Emitting Diode and Methylene Blue.

Background and aims The prevalence of pathogenic Escherichia coli as well as E. coli O157 and antibiotic- resistant bacteria has increased. This study aimed to examine the effect of methylene blue (MB) with sodium bicarbonate (NaHCO3) against E. coli using photodynamic antimicrobial chemotherapy (PACT). Materials and methods MB was basified using NaHCO3. E. coli and basic MB were smeared on the culture media followed by irradiation using a red light-emitting diode (LED) at 660 nm. Energy densities of 5, 10, 15, and 20 J/cm2 were applied to the culture medium.After 24 h, the bactericidal effect of basic MB with LED irradiation was determined based on the bacterial growth. Results The basic effect was observed with 1%-6% of NaHCO3 at 5 J/cm2.This effect increased between 1% and 2% of NaHCO3 at 10 J/cm2 and 15 J/cm2, whereas decreased at the NaHCO3 concentrations of > 2%. Moreover, this effect decreased at an energy density of 20 J/cm2. The biphasic basic effect on bactericidal activity was observed between pH 8.6-9.0. Conclusions Thus, PACT using basic MB may be an effective method for pathogenic E. coli sterilization.