Searching for New Natural Compounds of Microbial Origin with Efficacy Against Listeria monocytogenes Biofilm Formation

Listeria monocytogenes causes listeriosis, a relatively rare but severe disease associated with high mortality rates, particularly among in high-risk populations. To reduce its presence in food production environments and increase the microbiological safety of food by identifying and developing new compounds that inhibit L. monocytogenes biofilm formation, this work joins the methodology of high-throughput screening (HTS) with the search for innovative applications of microbial natural products. Experimental conditions of an in vitro HTS assay have been set up to detect microbial extracts with antibiofilm-forming activity against a reference strain of L. monocytogenes (EGD-e, ATCC BAA-679) susceptible to disinfectants. Activity has been assessed by measuring fluorescence using resazurin (a redox indicator that allows quantifying the cell viability in biofilms). So far, 1520 microbial extracts have been tested, 127 of which have been selected based on their activity profile against the EGD-e strain. Subsequently, these extracts have been tested against a panel of five strains of L. monocytogenes resistant to disinfectants and persistently isolated from the meat industry, and their chromatographic profiles have been examined to prioritize their further study according to their activity and the presence of already known molecules. Twelve extracts have shown broad inhibition biofilm formation against the five resistant strains and three of them are candidates for further bioactivity-guided fractionation and structural elucidation. Further work is underway to characterize the chemical composition of these three extracts and explore their potential applications, with the aim of developing natural biocide formulations that may have a reduced environmental impact.