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.