In vitro Photodynamic Action of Methylene Blue on Trypanosoma brucei.

In reviewing the literature dealing with the in vitro photodynamic action of acridine dyes on microörganisms, one is impressed with the fact that adequate study of this action on protozoa has yet to be made. The few reports in existence deal almost exclusively with the effect of the photodynamic action of various dyes on the motility of a few protozoa. Such were the studies made with Leishmania donovani flagellates by Noguchi 1 and those of trypalavine on Trypanosoma brucei by Tappeiner, 2 Bruynoghi, 3 and Jancso. 4 It seems plausible that motility alone cannot be taken as the criterion of life or death of the treated organisms. In addition, it is not inconceivable that such action might bring about some morphological changes on the treated protozoa. With these views in mind, it was considered of interest to restudy the in vitro photodynamic action on Trypanosoma brucei with methylene blue, a dye which hitherto has not been tried on this organism.

Citrated blood of guinea pigs infected with Trypanosoma brucei was diluted with normal saline. After the cells had been removed by centrifugation at low speed, the supernatant fluid which contained the organisms was mixed with various dilutions of saturated solution of methylene blue in the ratio of 9 to 1 respectively. Part of the mixture contained in a Petri dish was put over a Frigidaire cooling machine and exposed to a 100-Watt lamp at a distance of 10 cm. for one hour.