Transcriptomic insights into hydrogen peroxide-mediated antibacterial activity of Enterococcus lactis FSEL1 in raw milk biofilms

This study investigates the bactericidal potential of Enterococcus lactis FSEL1, isolated from raw milk, against major raw milk pathogens including Staphylococcus aureus, Listeria monocytogenes, and Escherichia coli O157:H7. The genome of E. lactis FSEL1 was sequenced, revealing a circular chromosome and two plasmids. Comparative genomic analysis showed that FSEL1 is genetically distinct from E. faecium and closely related to reference E. lactis strains, supporting its classification as E. lactis. Co-culture biofilm assays demonstrated the antimicrobial activity of E. lactis FSEL1, with significant reductions in S. aureus and L. monocytogenes, particularly in milk. Genes encoding bacteriocins such as enterolysin A and enterocin P were identified. Transcriptomic analysis revealed hydrogen peroxide as a key antimicrobial factor against E. coli O157:H7, further supported by in vitro quantification and scavenger assays. The strain lacked key virulence genes and carried only acm, suggesting low virulence potential. A bacteriocin gene with high sequence similarity to the lactococcin 972 family protein was significantly upregulated under co-culture conditions. These findings highlight E. lactis FSEL1 as a natural antimicrobial agent with strong potential for food safety and preservation.