Novel approach to controlSalmonella entericaby modern biophotonic technology: photosensitization

Abstract

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. Methods and Results: Salmonella enterica was incubated with ALA (7·5 mmol l−1) for 1–4 h and afterwards illuminated with visible light. The light source used for illumination of S. enterica emitted light λ = 400 nm with energy density 20 mW cm−2. The illumination time varied from 0 to 20 min and subsequently a total energy dose reached 0–24 J cm−2. The data obtained indicate that S. enterica is able to produce endogenous photosensitizer PpIX when incubated with ALA. Remarkable inactivation of micro‐organisms can be achieved (6 log) after photosensitization. It is obvious that photosensitization‐based inactivation of S. enterica depends on illumination as well as incubation with ALA time. Conclusion: ALA‐based photosensitization can be an effective tool against multi‐drug resistant Gram‐negative bacteria S. enterica serovar Typhimurium. Significance and Impact of the Study: Experimental data and mathematical evaluations support the idea that ALA‐based photosensitization can be a useful tool for the development of nonthermal food preservation technology in future.

Potential applications of porphyrins in photodynamic inactivation beyond the medical scope

“…Increasing the concentration to 7.5 mM and the incubation time to 30 min caused 2.7 log decrease on spores adhered to packaging [55]. An efficient inactivation (6 log) of Salmonella enterica serovar Typhimurium resistant to tetracycline (10 7 CFU mL −1 ) was achieved after 60 min incubation with 7.5 mM of 5-ALA and 20 min irradiation (24 J cm −2 ) [54]. In the case of L. monocytogenes, in vitro tests showed that cells were inactivated by 4 logs with 7.5 mM 5-ALA, incubated 120 min and irradiated 20 min.…”

“…The different effectiveness between photosensitization of biofilms and the cells adhered to the surface of packaging material was explained by the polysaccharide matrix of biofilms acting as a diffusion barrier for PS and reducing its accumulation inside bacteria [53]. The fluorescence intensity analysis of endogenous PS in these three microorganisms revealed that B. cereus produces endogenous porphyrins 10 times more efficiently than L. monocytogenes or S. enterica [54,100], explaining its higher susceptibility to 5-ALA-based photosensitization compared to the other two bacteria.…”

“…• the size of the N-alkyl chain on the porphyrin structure as shown on the photoinactivation of fungi spores, mainly by affecting their binding to cellular material [105]; • initial concentration, in the case of 5-ALA [55], and incubation time (or concentration of endogenously produced porphyrins) [53][54][55].…”

“…The experimental approach used in the studies below was the same already described for 5-ALA [53][54][55]. NaChl (0.075-75 M) was tested against B. cereus (10 7 CFU mL −1 ) vegetative cells and spores, in vitro or attached to the surface of packaging material, incubated 2-60 min and irradiated with visible light (20 mW cm −2 ).…”

High‐Intensity 405 nm Light Inactivation of Listeria monocytogenes

“…Similar approaches using preincubation with ALA to achieve photosensitization-based inactivation has also been used to achieve enhanced inactivation of other bacteria including Bacillus cereus (30) and S. enterica (31).…”