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- Author or Editor: Gabriella Kiskó x
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Abstract
Micro-organisms can attach to food surfaces and develop biofilms which present a concern in food and environmental safety. The main goal of the current study was to investigate the biofilm formation of six non-pathogenic Listeria strains under different stress conditions using a microplate assay. The effect of the weak biofilm-forming non-pathogenic Listeria strains on the biofilm formation of a strong biofilm-forming pathogenic Listeria strain (Listeria monocytogenes #8) was also examined. Listeria innocua CCM4030, Listeria innocua 2885 and Listeria seeligeri/welshimeri 292 showed the same patterns of biofilm formation with increasing NaCl concentrations from 0.05 to 15%, but all the other strains showed a continuously decreasing trend of OD595 in the same conditions. This study showed that in the case of non-pathogenic Listeria strains, higher concentrations of NaCl do not present a stress condition that enhances biofilm formation. Decrease in pH inhibited biofilm formation for all the non-pathogenic Listeria strains. The weak biofilm forming non-pathogenic Listeria strains (Listeria innocua 2885 and Listeria innocua CCM4030) overgrew the strong biofilm-forming Listeria strain (Listeria monocytogenes #8) during biofilm formation. This phenomenon could be beneficial and potentially be used as a novel control strategy to prevent the colonization of the pathogenic Listeria at food processing facilities such as in meat industry.
Abstract
This work aimed to study the antimicrobial activity of eight various components of plant origin on the growth of Pseudomonas lundensis and Listeria monocytogenes. Different in vitro methods were used: agar plate diffusion, micro atmosphere, agar hole diffusion, micro-dilution, and gradient-plate method. In the first agar plate assay, p-cymene and γ-terpinene did not inhibit the growth of the tested bacteria therefore they were not used in further experiments. Both α-pinene and limonene were only partially effective, but these were screened only for their partial inhibition. The other four components completely inhibited the growth of the tested bacteria. Using the agar-well diffusion method showed that carvacrol and thymol were found to be the most effective active components, thymol had minimum inhibitory concentration (MIC) at 1.563 mg/mL, however, in the case of carvacrol, MIC was 7.813 μL/mL. Additionally, eugenol and camphor show the same results but in higher concentrations. Gradient plate method was used to determine MIC values, in which it has been proved that carvacrol and thymol possess strong antimicrobial activity, no growth of tested bacteria was observed with carvacrol (100 μL/mL), while thymol exhibited MIC of 1.887 mg/mL against P. lundensis and 0.943 mg/mL needed to show complete inhibition of Listeria monocytogenes. Further experiments are needed to determine the optimum concentrations of the active components against P. lundensis and L. monocytogenes.
Abstract
Listeria monocytogenes is able to form biofilms on food contact surfaces. Effectiveness of salt concentration, pH, and temperature on the formation of L. monocytogenes biofilms was evaluated individually and in combinations using microtiter plate assay by measuring the optical density. The tested strains differed in their biofilm formation (low, moderate, and strong) ability. At 37 °C, decreasing amounts of biofilms was observed in almost all L. monocytogenes strains when the NaCl concentration increased from 0.05 to 15%, but all strains were able to form biofilm even at 1 °C. There was no significant difference in biofilm formation between pH 4, 5, and 6, except for some strains. When stress conditions were tested in combination, the addition of 15% NaCl significantly inhibited the growth of L. monocytogenes at 1 °C and 4 °C, and the weak biofilm-forming strains were less sensitive to the temperature and to NaCl treatments than the strong biofilm-forming strains. These results enhance our knowledge of the application of NaCl, temperature, and pH stresses in the food industry and provide basis to develop new strategies for control of biofilm formation of this pathogen.
