Bactericidal effects induced by laser irradiation and haematoporphyrin against gram-positive and gram-negative microorganisms.

Laser irradiation of tissues treated in vivo with haematoporphyrin (Hpr) is known to result in a cytocidal effect, reportedly more pronounced in tumour tissues. To ascertain whether this cytocidal phenomenon can occur not only in eukaryotic but also in prokaryotic cells, the authors devised a model system in vitro consisting of bacterial cultures in liquid and in solid media. Bacteria photosensitized with Hpr were subsequently exposed to laser beams and to daylight; then normal microbiological techniques were used to determine whether any bactericidal effect occurred. Satisfactory results were achieved, particularly against Gram-positive microorganisms; a partial inhibition of Gram-negative microorganisms was also observed.