Comparison of the methylene blue and toluidine blue photobactericidal efficacy against gram-positive and gram-negative microorganisms.
OBJECTIVE
Studies on the photobactericidal efficacy of methylene 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 the most effective bactericidal dye.


METHODS
Suspensions of Staphylococcus aureus, Streptococcus pneumoniae, Enterococcus faecalis, Hemophilus influenzae, Escherichia coli, and Pseudomonas aeruginosa in saline were treated in dark and red laser light conditions in the presence of each dye using an argon pumped-dye and a diode laser emitting light at 630 and 664 nm, respectively. The effect of dye concentration, dark incubation time, the fluence and intensity 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 concentrations of 1.5-7-fold less than that of MB.


CONCLUSIONS
TB exhibits a greater bactericidal activity than MB against most bacteria in dark and light conditions. Mostly, these results are consistent with their respective dye partition coefficients.
Usacheva
M N
MN
Advanced Photodynamic Technologies, Inc., 2715 4th Street SE, Suite 70, Minneapolis, MN 55414, USA.
Teichert
M C
MC
Biel
M A
MA
D004396:Coloring Agents; D006090:Gram-Negative Bacteria / Q000187:drug effects*; D006094:Gram-Positive Bacteria / Q000187:drug effects*; D007834:Lasers; D008751:Methylene Blue / Q000494:pharmacology*; D017319:Photosensitizing Agents / Q000494:pharmacology*; D014048:Tolonium Chloride / Q000494:pharmacology*
D004396:Coloring Agents; D017319:Photosensitizing Agents; D014048:Tolonium Chloride; D008751:Methylene Blue