This study is focused on the analysis of extracellular DNA (eDNA) from a biofilm matrix formed by Staphylococcus aureus, Listeria monocytogenes, and Salmonella enterica. The presence of eDNA in the biofilm of all the studied strains was confirmed by confocal laser scanning microscopy using fluorescent dyes with high affinity to nucleic acid. The protocol for eDNA isolation from the biofilm matrix was established, and subsequent characterization of the eDNA was performed. The purified eDNA obtained from the biofilm matrix of all three microorganisms was compared to the genomic DNA (gDNA) isolated from relevant planktonic grown cells. The process of eDNA isolation consisted of biofilm cultivation, its collection, sonication, membrane filtration, dialysis, lyophilisation, and extraction of DNA separated from the biofilm matrix with cetyltrimethylammonium bromide. An amplified fragment length polymorphism (AFLP) was used for comparing eDNA and gDNA. AFLP profiles showed a significant similarity between eDNA and gDNA at the strain level. The highest similarity, with a profile concordance rate of 94.7% per strain, was observed for S. aureus, L. monocytogenes, and S. enterica exhibited lower profiles similarity (78% and 60%, respectively). The obtained results support the hypothesis that the eDNA of studied bacterial species has its origin in the gDNA.
Extracellular DNA (eDNA) is an abundant matrix component that protects biofilm from environmental stress, facilitate horizontal gene transfer, and serve as a 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 in terms of phylogenetic relatedness. This study aims to determine if these variations exist. Biofilm forming capacity of ten L. monocytogenes strains of different phylogenetic lineages and serotypes was examined using crystal violet assay at 37°C and 22°C. eDNA content was evaluated fluorometrically at 37°C and at 22°C, then the 3D structure of biofilm was studied by confocal laser scanning microscopy (CLSM). Biofilm forming capacity differed significantly between the culturing conditions and was higher at 37°C than at ambient temperature. eDNA signal distribution was found to be influenced by strain and lineage. CLSM images revealed information about spatial distribution in the biofilm. The information about the eDNA spatial organisation in the biofilm contributes to the understanding of the role of eDNA in a biofilm formation.
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