Lactic Acid Bacteria (LAB) and Their Bacteriocins for Applications in Food Safety Against Listeria monocytogenes

Abstract

Background/objectives: Listeria monocytogenes is a major foodborne pathogen responsible for listeriosis, a serious illness with high morbidity and mortality, particularly in vulnerable populations. Its persistence in food processing environments and resistance to conventional preservation methods pose significant food safety challenges. Lactic acid bacteria (LAB) offer a promising natural alternative due to their antimicrobial properties, especially through the production of bacteriocins. This study investigates the competitive interactions between Lactococcus lactis and L. monocytogenes under co-culture conditions, with a focus on changes in their secretomes to better understand how LAB-derived bacteriocins can help mitigate the Listeria burden.

Methods: Proteomic approaches, including Tricine-SDS-PAGE, two-dimensional electrophoresis, and shotgun proteomics, were employed to analyze the molecular adaptations of both species in response to bacterial competition.

Results: Our results reveal a significant increase in the secretion of enolase by L. monocytogenes when in competition with L. lactis, suggesting its role as a stress-responsive moonlighting protein involved in adhesion, immune evasion, and biofilm formation. Concurrently, L. lactis exhibited a shift in the production of its bacteriocin, nisin, favoring the expression of Nisin Z-a variant with improved solubility and diffusion properties. This differential regulation indicates that bacteriocin production is modulated by bacterial competition, likely as a defensive response to the presence of pathogens.

Conclusions: These findings highlight the dynamic interplay between LAB and L. monocytogenes, underscoring the potential of LAB-derived bacteriocins as natural biopreservatives. Understanding the molecular mechanisms underlying microbial competition could enhance food safety strategies, particularly in dairy products, by reducing reliance on chemical preservatives and mitigating the risk of L. monocytogenes contamination.

Keywords: Listeria monocytogenes; bacteriocins; lactic acid bacteria; microbial competition; proteomics.

Figure 1

(a) Tricine-SDS-PAGE analysis of low molecular weight proteins. (b) One-dimensional electrophoresis of the three experimental replicates for each experimental group. MALDI-TOF analysis on bands indicated by arrows 1 and 2 highlighted the presence of enolase. Legend for both figures: M: molecular weight marker; BHI: brain heart infusion broth; LAB: lactic acid bacteria; LM: L. monocytogenes.

Figure 2

Two-dimensional maps of the cell filtrates from the three different experimental groups: (a) BHI medium with no bacterial growth; (b) cell filtrate of L. lactis; (c) cell filtrate of L. monocytogenes; and (d) cell filtrate of the co-culture of both bacteria. Mass spectrometry analysis identified the protein indicated by the arrow, which is expressed only in the co-culture condition, as the bacterial enolase of L. monocytogenes.

Figure 3

(a) Shotgun proteomics analysis results showing the differential representation of Enolase from L. monocytogenes alone and in competition conditions expressed in ng/mL. (b) Shotgun proteomics analysis results showing the differential representation of nisin lantibiotic forms A and Z in LAB alone and in competition conditions (LM + LAB) expressed in ng/mL.

Figure 4

Pairwise structure comparison of Nisin A (a) and Nisin Z (b) obtained with alphafold (https://alphafold.ebi.ac.uk/entry/P13068 (accessed on 10 May 2025)) starting from PDB models. The red arrows indicate the histidine residue of Nisin A and the asparagine residue of Nisin Z.