HEMATOPORPHYRIN‐SENSITIZED PHOTOINACTIVATION OF Streptococcus faecalis

Abstract— The photosensitizing action of hematoporphyrin (HP) on the cells of some bacterial strains belonging to the species Streptococcus faecalis, Staphylococcus aureus, Escherichia coli, and Klebsiella pneumoniae, as well as of strains of yeast Candida albicans, was studied in air‐equilibrated aqueous media at pH 7.2. All Gram‐negative strains appeared to be resistant even to prolonged irradiation both in the presence and in the absence of EDTA. On the other hand. Gram‐positive and yeast strains were photosensitive. In the case of Str. faecalis, whose strains displayed a particularly high photosensitivity, the efficiency of the photoprocess was mainly controlled by the HP concentration in the incubation medium (0.1‐1 μg/ml) and by the irradiation time (0–10 min); temperature (18–37oC) exerted a minor effect, whereas the incubation time (6–30 min) had no detectable influence. The photolability of Str. faecalis cells was only slightly different in the logarithmic and stationary phase of growth. The type of photoinduced ultrastructural modifications and the largely preferential binding of HP to the cytoplasmic membrane, as observed by cell fractionation studies, suggest that one important target of the HP‐photosensitized process is represented by membrane components.