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

Background and aims: The prevalence of pathogenic E scherichia 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.