The phototoxicity of phenothiazinium-based photosensitizers to bacterial membranes

Abstract

The ability of phenothiazinium-based photosensitizers to induce photodamage to Escherichia coli membranes is investigated. Phenothiazinium-based photosensitizers were found to be somewhat lipophilic (log P>0.7) and to induce surface-pressure changes (3-12 mN m-1) in lipid monolayers mimetic of bacterial membranes, implying that these molecules are able to penetrate biological membranes. Under dark and light conditions (3.15 J cm -1 for 30 min), phenothiazinium-based photosensitizers were incubated with E. coli cells. These cells showed levels of dark bacteriolysis that ranged between 6% and 13%, with light conditions leading to no significant increase in these levels. Gas chromatography-based analyses showed such incubations to produce no significant changes in the levels of C16 and C 18 fatty acid chain saturation found in E. coli whole lipid-extracts. It is concluded that the phenothiazinium-based photosensitizers studied may not use E. coli membranes as their primary photodynamic target, but may inflict photodamage on cytoplasmic targets, possibly DNA. © 2005 Federation of European Microbiological Societies. Published by Blackwell Publishing Ltd. All rights reserved.