A comparative study of the photoinactivation of bacteria by meso -substituted cationic porphyrin, rose Bengal and methylene blue

International audienceAdvances in wastewater treatment technology have led many to predict that planned wastewater reuse in agriculture will soon become more common in some regions of the world which face acute problems of water quality and quantity. The use of ecologically friendly wastewater disinfection techniques could be one of the most exciting advances in this field. The combined action of a photosensitizer (meso-substituted cationic porphyrin, TMPyP; rose Bengal, RB; methylene blue, MB) and visible light, particularly sunlight, seem to be a promising approach to microbial inactivation, potentially applicable for disinfection of domestic effluents. In the present work, photosensitization was either performed on Gram-positive and Gram-negative bacteria in pure culture (Enterococcus hirae and Escherichia coli), or carried out with wild strains in secondary wastewater effluent (enterococci and E. coli). The results described in this paper show that TMPyP is the most effective for photoinactivation of the bacterial models studied here. The relative effectiveness of RB and MB was found to be tightly linked to bacteria Gram type. Whatever the sensitizer used, Gram-negative bacteria were more resistant to photosensitization than Gram-positive strains. The order of increasing effectiveness of the photosensitizers for photoinactivation of Gram-positive bacteria (TMPyP ≥ RB > MB) and Gram-negative bacteria (TMPyP > MB > RB) remains unchanged for either pure culture or wild strains (bacterial communities in wastewater). The effectiveness of the photochemical process depends primarily on the type of microorganisms as well as the type of photosensitizers (concentration, singlet oxygen quantum yield, ionic charge), and the reaction medium

Photoinactivation de bactéries d intérêt sanitaire en condition de simulation solaire en présence de photosensibilisants synthétiques et/ou naturels

La photosensibilisation utilise une substance promotrice de l activité désinfectante de la lumière solaire faisant intervenir les espèces réactives de l oxygène. Dans ce travail nous avons retenu une porphyrine cationique (TMPyP). Pour cerner les facteurs de l efficacité de la désinfection des eaux usées, nous avons étudié les mécanismes de photoinactivation des bactéries. Les bactéries Gram-négatif (Escherichia coli) apparaissent plus résistantes à la photoinactivation que les bactéries Gram-positif (Enterococcus hirae). La même observation est réalisée sur des bactéries sauvages dans un effluent d eau usée. Les essais en résonance paramagnétique électronique (RPE) montrent que la TMPyP est susceptible d agir sur des substrats via les réactions de type I (espèces radicalaires) ou de Type II (oxygène singulet). La comparaison de l action de photosensibilisants synthétiques ou naturels à celle de la TMPyP montre que ce dernier est plus efficace pour la photoinactivation des bactéries. L efficacité du processus est lié au type de microorganismes, à la concentration et la charge électronique du photosensibilisant et à la charge organique du milieu.RENNES1-BU Sciences Philo (352382102) / SudocSudocFranceF

Involvement of both Type I and Type II mechanisms in Gram-positive and Gram-negative bacteria photosensitization by a meso-substituted cationic porphyrin

International audienceA meso-substituted cationic porphyrin (TMPyP) showed a photocytotoxicity against Gram-positive and Gram-negative bacteria. In order to determine the mechanism involved in the phototoxicity of this photosensitizer, electron paramagnetic resonance (EPR) experiments with 2,2,6,6-tetramethyl-4-piperidone (TEMP), a specific probe for singlet oxygen, and the spin-trap 5,5-dimethyl-1-pyrroline-N-oxide (DMPO) were carried out with illuminated TMPyP. An EPR signal characteristic of TEMP-singlet oxygen (TEMPO) adduct formation was observed, which could be ascribed to singlet oxygen (1O2) generated by TMPyP photosensitization. The signal for the DMPO spin adduct of superoxide anion (DMPO-OOH) was observed in DMSO solution but not in aqueous conditions. However, an EPR spectrum characteristic of the DMPO-hydroxyl radical spin adduct (DMPO-OH) was observed in aqueous conditions. The obtained results testify a primary hydroxyl radical ({radical dot}OH) generation probably from superoxide anion (O2{radical dot} -) via the Fenton reaction and/or via Haber-Weiss reaction. Gram-positive and Gram-negative bacteria inactivation by TMPyP photosensitization predominantly involved Type II reactions mediated by the formation of 1O2, as demonstrated by the effect of quenchers for 1O2 and scavengers for {radical dot}OH (sodium azide, thiourea, and dimethylsulphoxide). Participation of other active oxygen species cannot however be neglected since Type I reactions also had a significant effect, particularly for Gram-negative bacteria. For Gram-negative bacteria the photoinactivation rate was lower in the presence of superoxide dismutase, a specific O2{radical dot} - scavenger, and/or catalase, an enzyme which specifically eliminates H2O2, but was unchanged for Gram-positive bacteria. The generation of 1O2, O2{radical dot} - and {radical dot}OH by TMPyP photosensitization indicated that TMPyP maintained a photodynamic activity in terms of Type I and Type II mechanisms