The growing resistance against
antibiotics demands the search for alternative treatment strategies.
Photodynamic therapy is a promising candidate. The natural intermediate of
chlorophyll biosynthesis,
protochlorophyllide, was produced, purified and tested as a novel
photosensitizer for the inactivation of five model organisms including Staphylococcus aureus, Listeria monocytogenes and Yersinia pseudotuberculosis, all responsible for serious clinical
infections. When microorganisms were exposed to white light from a
tungsten filament lamp (0.1 mW cm(-2)), Gram-positive S. aureus, L. monocytogenes and Bacillus subtilis were photochemically inactivated at concentrations of 0.5 mg L(-1)
protochlorophyllide. Transmission electron microscopy revealed a disordered septum formation during cell division and the partial loss of the cytoplasmic cell contents. Gram-negative Y. pseudotuberculosis and Escherichia coli were found to be insensitive to
protochlorophyllide treatment due to the permeability barrier of the outer membrane. However, the two bacteria were rendered susceptible to eradication by
protochlorophyllide (10 mg L(-1)) upon addition of
polymyxin B nonapeptide at 50 and 20 mg L(-1), respectively. The release of
DNA and a detrimental rearrangement of the cytoplasm were observed.