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The Chemical Educator

ISSN: 1430-4171 (electronic version)

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Abstract Volume 10 Issue 2 (2005) pp 126-129

A New Antibacterial Approach Using Photodynamic Inactivation

Mariana B. Spesia, Marisa Rovera, Liliana Pascual, and Edgardo N. Durantini*,†

Departamento de Química and Departamento de Microbiología e Inmunología, Universidad Nacional de Río Cuarto, Agencia Postal Nro 3, X5804BYA Río Cuarto, Argentina,
Received October 15, 2004. Accepted January 27, 2005.

Published online: 11 February 2005

Abstract. A convenient procedure is shown to visualize the photodynamic inactivation (PDI) of bacteria sensitized by porphyrins. These experiments can be used as either an undergraduate project for natural-science advanced students or for a postgraduate practical-training course. The effects produced by cationic (5,10,15,20-tetra(4-trimethylammoniumphenyl)porphyrin iodide) and anionic (5,10,15,20-tetra(4-sulphonatophenyl) porphyrin) sensitizers are compared in vitro for a typical Gram-negative bacterium, Escherichia coli. The cells are incubated with 1 mM of sensitizer for 30 min and irradiated with visible light. Under these conditions, a higher photoinactivation of cells is found for cationic porphyrin, which causes a ~4.5 log (99.995 %) decrease in cell survival after 5 min of irradiation, whereas no toxicity is observed under dark conditions. On the other hand, the anionic porphyrin does not produce appreciable photodamage. The results can also be confirmed by growth-delay experiments. Finally, the ability of porphyrins to bind to bacterial cells can be determined to show the importance of cationic charge in the sensitizer. This methodology can be used to show the PDI of bacteria in a laboratory experiment.

Key Words: Laboratories and Demonstrations; photophysical chemistry; photoinactivation; porphyrin; bacteria; sensitizers

(*) Corresponding author. (E-mail:

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Issue date: April, 1 2005

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