Porphyrin derivatives as photosensitizers for the inactivation ofBacillus cereusendospores

Abstract

Aims: In this study, we propose (i) to study the photodynamic inactivation (PDI) efficiency of neutral and cationic porphyrin derivatives, (ii) to characterize the kinetics of the inactivation process using Bacillus cereus as a model endospore‐producing bacterium and (iii) to conclude on the applicability of porphyrin derivatives in the inactivation of bacterial endospores. Methods and Results: The study of PDI of Bacillus cereus endospores, taken as model‐endospores, using porphyrin derivatives differing in the number of positive charges and in the meso‐substituent groups, showed that neutral, monocationic and dicationic porphyrins are quite ineffective, in contrast with the tri‐ and tetra‐cationic molecules. The most effective porphyrin is a tricationic porphyrin with a meso‐pentafluorophenyl group. With this photosensitizer (PS), at 0·5 μmol l−1, a reduction of 3·5 log units occurs after only 4 min of irradiation. None of the porphyrin derivatives showed toxicity in the absence of light. Conclusions: Some porphyrin derivatives are efficient PSs for the inactivation of bacterial endospores and should be considered in further studies. Small modifications in the substituent groups, in addition to charge, significantly improve the effectiveness of the molecule as a PS for endospore inactivation. Significance and Impact of the Study: Tetrapyrrolic macrocycles should be regarded as worthy to explore for the PDI of spore‐producing gram‐positive bacteria. The development of molecules, more selective and effective, emerges as a new objective.

Photodynamic inactivation of Escherichia coli with cationic meso-tetraarylporphyrins – The charge number and charge distribution effects

“…The selection of these groups was based on our previous results with the tricationic porphyrin 4a that showed to be highly efficient in the photoinactivation of a wide range of microorganisms, namely bacteria, bacteriophages and bacillus endospores [22,37,[39][40][41][42][43]. The Gram-negative bacterium E. coli was selected for this work.…”

Potential applications of porphyrins in photodynamic inactivation beyond the medical scope

“…Since 2004, our research group has developed a broadspectrum of PS, namely cationic porphyrins, which can efficiently inactivate bacteria [18,71], bacterial endospores [135], viruses [17,35,136] and fungi [105]. One of the most effective compounds, a tricationic porphyrin with a pentafluorophenyl group (5,10,15-tris(1-methylpyridinium-4-yl)-20-(pentafluorophenyl)porphyrin tri-iodide, Tri-Py + -Me-PF), has been tested on bacteria and viruses to check the viability recovery and resistance development after repeated incomplete photoinactivation cycles.…”

Bacterial imaging and photodynamic inactivation using zinc(ii)-dipicolylamine BODIPY conjugates

“…The literature on spore resistance to PDI is mixed with reports citing various degrees of sporicidal effect. 58–60 Complete spore inactivation requires damage to the bacterial DNA or disruption of the inner membrane which is vital for the spore to undergo vegetative cell transition. 61 The DNA and inner membrane within the spore core are surrounded by layers of lipids and proteinaceous architecture that inhibit PS penetration.…”