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Aims:  The aim of this study was to evaluate the inactivation efficiency of Listeria monocytogenes ATCL3C 7644 and Salmonella enterica serovar Typhimurium strain DS88 by combined treatment of hypericin (Hyp)‐based photosensitization and high power pulsed light (HPPL). Methods and Results:  Cells were incubated with Hyp (1 × 10−5 or 1 × 10−7 mol l−1) in PBS and illuminated with a light λ = 585 nm. For the combined treatment, bacteria were, after photosensitization, exposed to 350 pulses of HPPL (UV light dose = 0·023 J cm−2). Fluorescence measurements were performed to evaluate optimal time for cell–Hyp interaction. Results indicate that Hyp tends to bind both Listeria and Salmonella. After photosensitization treatment, Listeria population was reduced 7 log, whereas Salmonella was inactivated just 1 log. Electron photomicrograps of Salmonella and Listeria confirmed that photosensitization induced total collapse of the Listeria cell wall, but not that of Salmonella. After combined photosensitization–HPPL treatment, the population of Listeria was diminished by 7 log and Salmonella by 6·7 log. Conclusions:  Listeria can be effectively inactivated by Hyp‐based photosensitization (7 log), whereas Salmonella is more resistant to photosensitization and can be inactivated just by 1 log in vitro. Combined treatment of photosensitization and pulsed light inactivates effectively (6·7–7 log) both the Gram‐positive and the more resistant to photosensitization Gram‐negative bacteria. Significance and Impact of the Study:  A new approach to combat Gram‐positive and Gram‐negative bacteria is proposed, combining photosensitization with high power pulsed light.

The silver nanoparticle colloid was used to obtain surface enhanced Raman spectra of Listeria monocytogenes, Salmonela enterica, and Esherichia coli bacteria. The SERS spectra were captured using for excitation the near-infrared (1064 nm) laser radiation with reduced intensity, which ensured the prevention of the fluorescence background as well as photo-and thermal decomposition of the samples. It was found that the optimal size of silver nanoparticles for the enhancement of the Raman signal in the near-infrared spectral region is ca. 50 nm. The spectral data obtained in this study indicate that relative intensities of SERS spectral bands of bacteria can be used for spectral differentiation of bacteria. In case of Listeria, Salmonela, and Esherichia cells, the intensity ratio of spectral bands of adenine and cysteine can be used as a spectral marker for differentiation of the bacteria.

Recently developed genetic methods, compared to the traditional morphological and biochemical tests, have been designated as the "gold standard" for bacterial identification. However, these methods are time-consuming and require expensive reagents and expendables. In this context, Raman spectroscopy is gaining increasing attention. Our study demonstrates FT Raman spectra of thermotolerant and thermoresistant Listeria monocytogenes species, applying silver nanoparticles for enhancing the Raman signal. The region 600-800 cm-1 of SERS spectra of pathogenic bacteria is best suited for the identification and discrimination of these two pathogenic bacteria.

Food-borne diseases have been estimated to cause millions of hospitalizations and cost billions of dollars each year. This means that the existing food safety technologies cannot guarantee safe food. The aim of this study was to evaluate the antimicrobial efficiency of photoactivated ZnO nanoparticles against the food pathogens Escherichia coli O157:H7 and Listeria monocytogenes ATC L3 C 7644. The results have shown ZnO NPs to have a slight effect on the viability of bacteria in the dark, whereas photoactivated ZnO NPs exhibit a pronounced bactericidal activity. In certain experimental conditions, gram-negative bacteria E. coli and gram-positive bacteria L. monocytogenes were killed to undetectable level. Summarizing, photoactivated ZnO NPs have a potential to be an effective antimicrobial tool and can be used to inactivate harmful and pathogenic microorganisms.