Irina Buchovec

Inactivation of food pathogen Bacillus cereus by photosensitization in vitro and on the surface of packaging material.

Aims:  The study was focused on the possibility to inactivate food pathogen Bacillus cereus by 5‐aminolevulinic acid (ALA) – based photosensitization in vitro and after adhesion on the surface of packaging material.

Inactivation of several strains of Listeria monocytogenes attached to the surface of packaging material by Na-Chlorophyllin-based photosensitization

This study was focused on the possibility to inactivate thermosensitive Listeria monocytogenes ATC(L3)C 7644 and thermoresistant 56 Ly strain by Na-Chlorophyllin (Na-Chl)-based photosensitization in vitro and on the surface of packaging. Comparative analysis of antimicrobial efficiency of photosensitization with conventional surface cleaning was performed. Data indicate that both Listeria strains, after incubation with Na-Chl and following illumination (λ=400nm, 20mWcm(-2)), were inactivated by 7 log in vitro. This treatment cleaned both Listeria strains from packaging surfaces. Comparative analysis indicates that washing with water diminishes pathogens by less than 1 log, 200ppm Na-hypochlorite by 1.7 log, Na-Chl-based photosensitization by 4.5 log. Listeria biofilms were totally removed from the surface by photosensitization at higher photosensitizer concentrations and longer incubation times. In conclusion, both strains of L. monocytogenes can be effectively inactivated by photosensitization in vitro and on the surface of packaging. Listeria biofilms are susceptible to this treatment as well. Comparison of different surface decontamination treatments reveals that photosensitization is much more effective against both Listeria strains than washing with water or 200ppm Na-hypochlorite. Our data support the idea that Na-Chl-based photosensitization is an effective antimicrobial tool which may serve in the future for the development of human and environmentally friendly surface decontamination techniques.

Photosensitization-based inactivation of food pathogen Listeria monocytogenes in vitro and on the surface of packaging material.

The study was focused on the susceptibility of Listeria monocytogenes ATCL3C 7644 cells and biofilms to non-thermal antimicrobial treatment - photosensitization in vitro and after adhesion to the surface of packaging material. L. monocytogenes was incubated with 5-aminolevulinic acid (ALA) (7.5 mM) for 0-2h and illuminated with visible light. The LED-based light source used for the illumination emitted light lambda=400 nm with energy density 20 mW/cm(2). The illumination time varied 0-20 min, and a total light dose reached 0-24 J/cm(2). The obtained data indicate that L. monocytogenes produces endogenous porphyrins after incubation with 7.5mM ALA. Subsequent illumination of cells remarkably inactivates (4 log) them in vitro. Photosensitization diminished population of Listeria cells adhered onto the packaging material by 3.7 log and inactivated bacterial biofilms by 3.1 log. It was shown that antimicrobial efficiency of photosensitization depended on the illumination time, incubation with ALA time as well as on the used ALA concentration. In conclusion, cells and biofilms of L. monocytogenes ATCL3C 7644 can be effectively inactivated by ALA-based photosensitization in the solution as well as adhered onto the surface of packaging material. Obtained data support the idea, that photosensitization as non-thermal and effective antimicrobial treatment has potential to develop into environmentally safe, surface decontamination technique.

Novel approach to control Salmonella enterica by modern biophotonic technology: photosensitization

Aims:  Salmonellosis is one of the most common foodborne diseases in the world. The aim of this study was to evaluate the antibacterial efficiency of 5‐aminolevulinic acid (ALA) based photosensitization against one of food pathogens Salmonella enterica.

Inactivation of Bacillus cereus by Na-chlorophyllin-based photosensitization on the surface of packaging

Aims:  This study was focused on the possibility to inactivate food‐borne pathogen Bacillus cereus by Na‐chlorophyllin (Na‐Chl)‐based photosensitization in vitro and after attachment to the surface of packaging material.

Inactivation of Gram (−) bacteria Salmonella enterica by chlorophyllin-based photosensitization: Mechanism of action and new strategies to enhance the inactivation efficiency

This study is focused on the enhancement of susceptibility of Gram (-) bacteria S. enterica to chlorophyllin-based (Chl) photosensitization combining it with other antimicrobial tools. In order to find best combinations, the mechanism by which Chl-based photosensitization inactivates bacteria must be identified. Data confirmed that photosensitization (Chl 1.5×10-5M, for 1-120min, 405nm, 0-46.1J/cm2) reduced S. enterica population, just by 2.05 log (CFU/ml). Fluorimetric measurements indicated that just minor part of Chl was bound to Salmonella in suspension. Addition of sodium azide (NaN3) (10mM) protected bacteria from killing, what means that 1O2 took place in photochemical reactions. Gene expression data confirmed that Chl-based photosensitization induced oxidative stress in bacteria cells, since mostly genes responsible for detoxification of ROS (OxyR, AhpC, GrxA) have been expressed in Salmonella. Moreover, the expression of genes, responsible for the inhibition of oxidative respiration (AtpC), cell division and down-regulation of metabolism (SulA) have been detected. In addition, Chl-based photosensitization induced significant release of intracellular components (absorbing at λ260 nm and λ280 nm) in bacteria that indicated increased membrane permeability. Thus, the combination of two antimicrobials (Chl-based photosensitization and chitosan (CHS)) with the same target (cellular membrane) in the presence of light drastically reduced viable Salmonella population (by 7.28 log). Combined treatment of photosensitization and high power pulsed UV light (HPPL) was also very effective, since reduced viable Salmonella by 7.5 log. Bacterial regrowth experiments clearly indicated that after both combined treatments Salmonella lost its ability to proliferate, and SEM images confirmed that after both treatments no viable bacteria have been found at all.