Comparison of the methylene blue and toluidine blue photobactericidal efficacy against gram-positive and gram-negative microorganisms

Background and Objective: Studies on the photobactericidal efficacy of meth ylene blue (MB) and toluidine blue (TB) have shown inconsistent results in the literature. This study evaluated the bactericidal efficacy of MB and TB against different bacteria under light and dark conditions to determine th e most effective bactericidal dye. Study Design/Materials and Methods: Suspensions of Staphylococcus aureus, S treptococcus pneumoniae, Enterococcus faecalis, Hemophilus influenzae, Esch erichia coli, and Pseudomonas aeruginosa in saline were treated in dark and red laser light conditions in the presence of each dye using an argon pump ed-dye and a diode laser emitting light at 630 and 664 nm, respectively. Th e effect of dye concentration, dark incubation time, the fluence and intens ity of laser light on the destruction of different bacteria were compared. Results: Both dyes eradicated all examined bacteria under laser light. The complete photodestruction of microorganisms was reached at TB concentration s of 1.5-7-fold less than that of MB. Conclusion: TB exhibits a greater bactericidal activity than MB against mos t bacteria in dark and light conditions. Mostly, these results are consiste nt with their respective dye partition coefficients. (C) 2001 Wiley-Liss, I nc.