Photobactericidal activity of methylene blue derivatives against vancomycin-resistant Enterococcus spp.

The toxicities and phototoxicities of methylene blue and its two methylated derivatives were measured against one standard and three vancomycin-resist ant pathogenic strains of Enterococcus spp, Each of the compounds was bacte ricidal and the derivatives exhibited photobactericidal activity on illumin ation at a 'light' dose of 6.3 J/cm(2) against one or more of the strains, Increased bactericidal and photobactericidal activity in the methylated der ivatives is thought to be due to their higher hydrophobicities allowing gre ater interaction with the bacterial cell wall, In addition, the derivatives exhibited higher inherent photosensitizing efficacies.