Studies on the Mechanism of the Photosensitized Inactivation of E. Coli and Reactivation Phenomenon

Abstract

Photosensitized inactivation of microorganisms has been the subject of numerous studies, and various hypothetical reaction mechanisms have been proposed for the interpretation of the phenomenon. In spite of such extensive experimentation and theorizing, there still exists uncertainty concerning the inactivation processes. No attempt will be made to review the subject since it has been analyzed and treated by Blum (1) and Arnow (2). It is evident that photosensitized inactivation is dependent on a variety of experimental factors. However, the literature reveals that the influence of such factors has been determined in many diverse and isolated experiments which makes the over-all evaluation of the data difficult, It was thought that, by studying a single system under various experimental conditions, a more satisfactory interpretation could be found. A methylene blue and E. coli system was selected, since the methylene blue oxidation-reduction cycle represents a reversible process, and the associated structural changes in the molecule are known. Experimental Metkods and Results Experimental Material and Irradiation Procedures.--E. coli B/r were grown inliquid synthetic M-9 medium (3) with aeration. The culture was centrifuged and resuspended in the desired solvent. Mter irradiation, assays were made by diluting the suspension in saline and plating on nutrient agar containing 4 × 10 -6 gin. per ml. of gentian violet.G. E. H-4 and DH-1 mercury lamps were used as irradiation sources. The test tubes containing the samples were placed in a water bath 5 cm. from the source. During the irradiation oxygen bubbled through the solution, providing a constant oxygen tension and continuous agitation of the suspension. Occasionally, different procedures were used. These will be described in other sections of the paper.The methylene blue used was u.s.1,, grade commercial product which contained not less than 98.5 per cent methylene blue chloride.

Photodynamic Inactivation of Bacteriophage

“…It seems reasonable to assume that the small amount of inactivation under anaerobic conditions was due to a residue of oxygen which was not removed. These results are in agreement with those of Heinmets et al (1952) and Oster and McLaren (1950). It is e*ident that molecular oxygen is essential for the photodynamic inactivation of bacteriophage, as has been found for most other photodynamic systems studied.…”

“…The effect of changes in dye concentration may be seen from figure 2. At low concentrations the inactivation rate is directly proportional to dye concentration, presumably because only adsorbed dye is effective in photodynamic inactivation (Heinmets et al, 1952) and the amount of dye adsorbed is proportional to its concentration. At higher concentrations the inactivation rate reaches a maximum and then decreases because the filtering effect of the dye decreases the effective light intensity.…”

Main Properties of the THERAFLEX MB-Plasma System for Pathogen Reduction

“…Subsequently different authors have described reduction of several pathogens to different extent. This includes Herpes simplex [28], Escherichia coli [29], and vaccinia virus [30]. Today it is well established that combined MB light system has a broad spectrum potential for reducing the impact of pathogens transmittable through transfusion.…”

The Effect of Temperature on the Conversion of Protochlorophyll to Chlorophyll a in Etiolated Barley Leaves.

“…Furthermore, at -700C, no activity was observed for any of the enzymes named during a 27-day period, while the photochemical transformation of protochlorophyll proceeded quite rapidly at this temperature. Because of these facts, it is concluded that the reaction is controlled by photochemical activation rather than by enzyme activation (2,3).…”