Food Microbiology

Extracellular DNA (eDNA) is an abundant matrix component that protects biofilm from the environmental stress, facilitate the horizontal gene transfer and serve as source of nutrients. eDNA is also found in Listeria monocytogenes biofilm, but it is unknown to which extent its importance as a matrix component varies from strain to strain. This study aims to determine if strain-specific variations exist, and if the role of eDNA in L. monocytogenes biofilms is dependent on the conditions under which the biofilm was formed. Biofilm forming capacity of 10 selected Listeria monocytogenes strains originating from food of different phylogenetic lineages and serotypes was examined using crystal violet assay. The strains were cultured under static condition in nutrient rich environment at 37 °C, and in low nutrient environment at ambient temperature. Biofilm forming capacity was evaluated by crystal violet assay, and the 3D structure of biofilm was studied by fluorescence staining and confocal microscopy. Extracellular DNA was quantified by PicoGreen® staining and fluorometric detection. Significant differences in biofilm forming capacity were found between the culturing conditions. There was a positive correlation between extracellular DNA production and total biomass under both culturing conditions and the significant difference was shown in extracellular DNA release between the conditions. Although extracellular DNA concentration was affected by biomass, confocal laser scanning microscopy (CLSM) images revealed information about spatial distribution in biofilm. Extracellular DNA signal distribution was found to be influenced by strain and lineage.