Photodynamic Action of Methylene Blue on Bacteria

Abstract

The effect of the prolonged use of photodynamically active dyes on a number of bacteria was summarized by Reitz. 1 Workers mixed the dyes and the cultures and let them stand for days exposed or unexposed to light. It was found that some dyes, including methylene blue, were more active in the presence of light than other dyes, such as fluorescein. It was also found that B. diphtheriae was more susceptible to such action than B. typhosus. Since then, however, very few reports have appeared. In view of the recent interest in the study of photodynamic action on viruses, bacteriophage, 2 and toxins, 3 it seems worthwhile to restudy this problem systematically.

We have studied the effect of short exposures to light of different dilutions of methylene blue on a number of Gram-positive and Gram-negative microorganisms. A preliminary report is presented at this time.

Saturated aqueous solution of methylene blue was diluted to different concentrations with normal saline. Twenty-four hour broth cultures of different organisms were mixed with these solutions in Petri dishes. The bacteria-methylene-blue mixtures were exposed to an ordinary electric light of 100 candle power at a distance of 10 cm. for a period of half an hour. These Petri dishes were placed on a cooling machine which prevents the plate from getting too warm. Soon after the exposure, the organisms were plated out and incubated. The other portions of the same mixtures were not exposed and were similarly plated to serve as controls.