Novel Approach to Effective and Uniform Inactivation of Gram-Positive Listeria monocytogenes and Gram-Negative Salmonella enterica by Photosensitization

Zivile Luksiene^1,2, Rita Kokstaite¹, Pranas Katauskis² and Vladas Skakauskas²*

¹Institute of Applied Research, Vilnius University, Sauletekio 10, LT-10223 Vilnius, Lithuania
²Faculty of Mathematics and Informatics, Vilnius University, Naugarduko 24, LT-03225 Vilnius, Lithuania

Article history:
Received May 10, 2012
Accepted November 5, 2012

Key words:
photosensitization, chlorophyllin, aminolevulinic acid, Salmonella enterica, Listeria monocytogenes

Summary:                                                                                                                                                                                 
The aim of this work is to compare the antimicrobial efficiency of aminolevulinic acid- -based photosensitization (ALA-photo) and chlorophyllin-based photosensitization (CHL- -photo) against Gram-positive Listeria monocytogenes and Gram-negative Salmonella enterica, to assess some quantitative inactivation parameters of their survival curves and to propose a strategy for their effective inactivation. Cells were incubated with CHL (7.5·10^–5–7.5·10^–8 M) or ALA (7.5 mM) and then illuminated with visible light (λ=400 nm). The analysis of bacterial survival curves indicates that Salmonella is more resistant to CHL-photo than to ALA-photo. The shoulder of the inactivation curve was longer and the population reduction suddenness was smaller than that after ALA-photo. Listeria was more sensitive to CHL-photo than to ALA-photo. No shoulder of the survival curves of Listeria was detected after CHL-photo. Examination of bacterial survival curves enabled the determination of the optimal experimental set-up for combined ALA- and CHL-photo treatments. The obtained results indicate that both Salmonella and Listeria were inactivated to an undetectable level when combined treatment was applied. Thus, combined ALA- and CHL- -photo treatment may be an effective tool to increase effective inactivation of both Gram(+) and Gram(–) food pathogens. Experimental results and the analysis of survival curves suggest innovative approach to combat Gram(+) and Gram(–) bacteria by photosensitization in effective and uniform way.  

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