Traditional Fermented Foods from Southern Brazil as a Source of Bacteriocinogenic Lactic Acid Bacteria against Listeria monocytogenes

Background: Traditional fermented foods are recognized as valuable reservoirs of lactic acid bacteria (LAB) with potential applications in food biopreservation. The aim of this study was to screen LAB isolates from artisanal food matrices produced in southern Brazil for bacteriocin-producing LAB active against Listeria monocytogenes.

Methods: A total of 200 LAB isolates obtained from traditional fermented foods produced in Santa Catarina, Southern Brazil—including colonial salami-type dry-fermented sausages, sheep's milk cheese, cow's milk cheese, and sourdough—were screened for antimicrobial activity against L. monocytogenes using the spot-on-lawn method. Cell-free supernatants from active isolates were subsequently evaluated for anti-Listeria activity. Active cell-free supernatants were neutralized with 0.1 M NaOH and digested with proteinase K to distinguish bacteriocin-mediated inhibition from the effects of organic acids and other metabolites. Selected isolates were further characterized by hemolytic profile, activity against other foodborne pathogens, growth under varying oxygen conditions, and MALDI-TOF MS identification.

Results: Among the 200 isolates, two Gram-positive, catalase-negative LAB isolates (1.0%) demonstrated notable inhibitory activity against L. monocytogenes. This inhibitory effect persisted following pH neutralization but was completely abolished after proteinase K treatment, confirming the proteinaceous nature of the antimicrobial compounds and suggesting the production of bacteriocin-like inhibitory substances. Both isolates were γ-haemolytic. MALDI-TOF MS identified the strains as Pediococcus acidilactici and Enterococcus mundtii. E. mundtii exhibited enhanced growth under aerobic conditions, whereas P. acidilactici showed better growth under microaerophilic conditions. Evaluation of the antimicrobial spectrum revealed no inhibitory activity against Escherichia coli, Pseudomonas aeruginosa, or Staphylococcus aureus, indicating a narrow antimicrobial spectrum primarily directed against L. monocytogenes.

Conclusions: Traditional fermented foods are a valuable source of bacteriocinogenic lactic acid bacteria. The P. acidilactici and E. mundtii isolates identified in this study exhibited promising anti-Listeria activity, suggesting their potential application as natural biopreservative cultures in food systems. Further studies will evaluate their safety and characterize the antimicrobial compounds.