Photobiological activity of exogenous and endogenous porphyrin derivativesin Escherichia coli and Enterococcus hirae cells

Photodynamic treatment, the combined application of a photosensitiser and v isible light, represents a new and promising approach for the inactivation of microorganisms. The photosensitising potentials of exogenous zinc-phthal ocyanine-tetrasulphonate (ZnPsTS), tetraphenylporphyrins (TPPs) and endogen ous porphyrin derivatives were tested and compared on Cram-negative and Gra m-positive bacteria, Escherichia coli B. and Enterococcus hirae, respective ly. The synthesis of endogenous porphyrins was induced by 5-aminolevulinic acid (delta -ALA). The porphyrin- or delta -ALA-treated cells were irradiat ed with white light. The photosensitising efficiency of endogenous derivati ves on both types of bacteria is ZnPcTS < TP(4-OGluOH)(3)P < TP(4-OGluOH)(4 )P. However, neither exogenous derivatives exhibit appreciable photosensiti sing activity for disinfection application. ALA-induced photodynamic treatm ent showed good potential for the inactivation of Escherichia coli cells, b ut not towards Enterococcus hirae cells. The failure of photosensitisation of the Enterococcus hirae strain selected indicates that apart from the Gra m-positive character, other structural elements of the membrane can influen ce the result of photodynamic treatments.