Maciej Nowak ¹ Zbigniew Paluszak ¹ Natalia Wiktorczyk-Kapischke ² Katarzyna Grudlewska-Buda ² Anna Budzyńska ² Joanna Skonieczna-Kurpiel ³ Ewa Walecka-Zacharska ³ Monika Huse-Kutowska ² Krzysztof Skowron ^2*

• ¹ Bydgoszcz University of Science and Technology, Bydgoszcz, Pomeranian, Poland
• ² Ludwik Rydygier Collegium Medicum in Bydgoszcz, Nicolaus Copernicus University in Toruń, Bydgoszcz, Poland
• ³ Wroclaw University of Environmental and Life Sciences, Wrocław, Poland

Listeria monocytogenes are Gram-positive, non-spore-producing rods that are the etiological agent of listeriosis. L. monocytogenes is isolated from soil, water, sewage, rotting vegetation, and the main source of these rods for humans is food. The aim of the study was to assess the frequency of L. monocytogenes in soil samples obtained from under organic carrot farming (Poland) and to characterize selected properties of the obtained strains. Twenty-seven L. monocytogenes isolates were isolated, from which 10 genetically different strains were isolated (PFGE method). 80% of the tested strains were sensitive to the tested antibiotics (disc-diffusion method). The highest invasiveness against HT-29 cells at 23.2% was shown for strain 11. The level of coaggregation between the tested strains and Salmonella Enteritidis ranged from 22.2% to 39.1%. The number of biofilm-isolated rods from the stainless steel surface was 6.37 to 7.10 colony-forming unit (CFU) × cm-2, while on polypropylene it was from 6.75 to 8.06 CFU × cm-2. The effectiveness of the disinfectants used depended on the duration of action and the concentration of the disinfectant. It was shown that organic food can be a source of L. monocytogenes. The research conducted may help in the introduction of standards regulating the safety of organic farming.