Comparative analysis of the photobactericidal action of selected tetrapyrrole compounds on Gram-positive and Gram-negative bacteria

Abstract

We have analysed the photobactericidal efficacy of four tetrapyrrole compounds on several strains of Gram-negative and Gram-positive bacteria. The bacterial cells were photosensitised with the following derivatives: uncharged meso-tetra(3-hydroxyphenyl)chlorin (mTHPC); cationic tetrakis (N-ethylpyridinium-4-yl) porphyrin tetratosylate (TN-Et-PyP); zinc phthalocyanine tetrasulfonate (ZnPcS4) and aluminium phthalocyanine tetrasulfonate (AlPcS4) (both anionic). The phototoxic activity of photosensitisers against all bacterial strains tested has been found to increase in the order AlPcS4< ZnPcS4< mTHPC< TN-Et-PyP. Gram-negative bacteria appeared to be more refractory to photodynamic action of all the tetrapyrrole derivatives tested. Gram-negative bacteria possessing a truncated lipopolysaccharide (LPS) chains were more sensitive to the phototoxic action of mTHPC than cells with wild-type LPS. Sensitivity of Gram-negative cells to photokilling by mTHPC could be enhanced by reducing the LPS content of bacterial cell envelope by Tris-EDTA treatment. Keywords: photodynamic antimicrobial chemotherapy (PACT), neutral, anionic and cationic photosensitisers, bacterial cell wall composition