Evaluation of potential bacteriocin-producing bacteria recovered from soil. A holistic OneHealth strategy against multidrug-resistant pathogens and for food-industry applications

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Introduction/Objective: Soils are reservoirs for a wide variety of bacteria, that coexist and compete for access to better nutrient sources by producing bacteriocins as a defense mechanism to a hostile ecosystem. These antimicrobial peptides would be of great interest for biomedical and food-industry applications. Therefore, the objective of this study was to evaluate the antimicrobial-activity (AA) of soil bacteria against a wide range of relevant pathogens.Material and Methods: Fifty-eight isolates recovered from soil samples were selected as potential bacteriocin-producing bacteria (P-Bac+) from a broad screening performed in La Rioja region during 2019-2023, linked to the “MicroMundo project”. They were identified by MALDI-TOF. The AA was confirmed by the spot-on-lawn method against 15 indicator-bacteria, including multidrug-resistant bacteria such as methicillin-resistant Staphylococcus aureus (MRSA) and Listeria monocytogenes, among other relevant pathogens. Antimicrobial- susceptibility testing of P-Bac+ was performed by the disk-diffusion method and β-hemolytic activity was also tested. Selected P-Bac+ strains were submitted to whole-genome- sequencing (WGS) for genomic characterization.Results: Fifty of the 58 isolates evaluated showed AA against at least one of the 15 indicator- bacteria tested and were considered as P-Bac+. They were of 13 genera and 25 species (genera(number isolates)): Bacillus(30), Pseudomonas(8), Brevibacillus(6), Paenibacillus(4), Streptomyces(2), Staphylococcus(1), Advenella(1), Arthrobacter(1), Brachybacterium(1), Klebsiella(1), Lysinibacillus(1), Microbacterium(1), and Peribacillus(1). Among P-Bac+ isolates, 51.4% were susceptible to all antibiotics tested and 67% lacked β-hemolytic activity. The Brevibacillus laterosporus strain MM3 revealed AA against 8/15 indicators tested with strong inhibitory activity against MRSA and L. monocytogenes. Ten isolates [Staphylococcus hominis/(1), Bacillus pumilus/safensis/altitudinis/mycoides/(5), Brevibacillus laterosporus(2), Paenibacillus apiarus(1) and Pseudomonas kilonensis(1)] were selected for WGS characterization (in process).Conclusions: Soils are reservoirs of bacteriocin-producing bacteria with antimicrobial-activity against relevant pathogens, which is of great interest for biomedical and food-industry applications.