Susceptibility of planktonic cultures of Streptococcus mutans to photodynamic therapy with a light-emitting diode

The objective of this study was to evaluate the effect of photodynamic therapy with erythrosine and rose bengal using a light-emitting diode (LED) on planktonic cultures of S. mutans. Ten S. mutans strains, including nine clinical strains and one reference strain (ATCC 35688), were used. Suspensions containing 10(6) cells/mL were prepared for each strain and were tested under different experimental conditions: a) LED irradiation in the presence of rose bengal as a photosensitizer (RB+L+); b) LED irradiation in the presence of erythrosine as a photosensitizer (E+L+); c) LED irradiation only (P-L+); d) treatment with rose bengal only (RB+L-); e) treatment with erythrosine only (E+L-); and f) no LED irradiation or photosensitizer treatment, which served as a control group (P-L-). After treatment, the strains were seeded onto BHI agar for determination of the number of colony-forming units (CFU/mL). The results were submitted to analysis of variance and the Tukey test (p < 0.05). The number of CFU/mL was significantly lower in the groups submitted to photodynamic therapy (RB+L+ and E+L+) compared to control (P-L-), with a reduction of 6.86 log10 in the RB+L+ group and of 5.16 log10 in the E+L+ group. Photodynamic therapy with rose bengal and erythrosine exerted an antimicrobial effect on all S. mutans strains studied.

Some naturally occurring phytophototoxins for mosquito control.

Alpha-terthiophene (alpha-T) and erythrosin-B, the naturally occurring plant secondary metabolites, were tried for their phototoxic properties against Anopheles and Culex larvae under dark, ordinary tube light (1.9-2.4 w/m2) and sun light (680-840 w/m2). LC50 values of alpha-T for Anopheles larvae (4th instar) were found to be 154, 92 and 11 ppb under dark, tube light and sunlight, respectively. For Culex larvae corresponding LC50 values under different light conditions were 129, 97 and 22 ppb. Erythrosin-B under all photoregimens was found to be less toxic to larvae of both Anopheles and Culex sps. Also, the susceptibility of the mosquito species decreased with age, towards alpha-T and erythrosin-B. Cumulative effects in terms of delay in metamorphosis were also observed among survivors of such exposures. The effects of these compounds were also seen on the adults and developing unhatched embryos of a common aquatic snail (Lymnaea sps). The LC50 values of alpha-T for adults were found to be 39, 23 ppm and 77 ppb under dark, tube light and sunlight and for developing unhatched embryos the corresponding values were 620, 41 and 13 ppb. Erythrosin-B was found to be much less toxic under sunlight and dark, to both adults and embryos as compared to the toxicity of alpha-T. Potential use of such biodegradable and eco-friendly compounds of natural origin in mosquito control is discussed.