Photodynamic Action of Various Dyes on Bacteria

Abstract

In the presence of ordinary visible light from an electric bulb, methylene blue was found to exert a rapid bactericidal action on certain bacteria which survived the same dye even in higher concentration in the absence of lamplight. 1 At the same time, gram negative bacilli were found to be highly resistant to this action of methylene blue. In continuation of a systematic study of photo-dynamic action of dyes on bacteria, various other common dyes have been chosen, and tests with representative gram positive and gram negative organisms repeated. The result of such a study is hereby presented.

Saline solutions of eosin, mercurochrome, acid fuchsin, basic fuchsin, and fluorescein, and a commercial 2% solution of trypa-flavine were used. Bacteria were grown on either blood- or plain meat-infusion agar for 24 hours and were then suspended in saline. Except in the case of trypaflavine, which was diluted with the suspension to the desired concentrations, suspensions were added to equal parts of dyes in the different dilutions recorded in Table I.

In order to facilitate the study of a large number of specimens at the same time, the procedure previously employed was slightly modified. Instead of petri dishes, sterile, hollow-ground slides with 2 cells each were used. The cells were protected with cover-slips which permitted maximal penetration of light from a 100-watt bulb 10 cm. distant. As in previous experiments, the slides were placed on a cooling machine which kept their temperature at or below 20°C. Controls were exposed to diffuse daylight at room-temperature. At intervals of 15, 30, and 60 minutes after exposure, samples were plated and examined for growth after 24 hours'incubation. The pertinent results of the photodynamic action of eosin, mercurochrome and trypaflavine after 60 minutes'exposure to lamplight are presented in Table I, while those from acid fuchsin, basic fuchsin, and fluorescein were omitted as these dyes were practically inert.