Effects of an enterocin-containing postbiotic on Listeria monocytogenes: phenotypic and transcriptional insights in a cheese-mimicking matrix

An enterocin-containing postbiotic (Ef–ECP) obtained from Enterococcus faecium RM12 was used to evaluate its impact on functional responses and gene expression of Listeria monocytogenes ATCC 19115. The minimum inhibitory concentration (MIC) of Ef-ECP at inhibitory (1 × MIC) and sub-inhibitory (½ × and ¼ × MIC) concentrations were tested. Under optimal laboratory conditions (BHI broth at 37 °C), Ef–ECP significantly impaired key phenotypic traits of L. monocytogenes. At 1 × MIC, Ef–ECP markedly inhibited motility (>57% reduction in swimming and swarming), reduced biofilm formation to below 25% of control levels with only partial eradication of preformed biofilms, and significantly decreased cell surface hydrophobicity and auto-aggregation even at sub-inhibitory concentrations. To evaluate the behaviour of Ef-ECP in food environments, a cheese-mimicking broth prepared from lyophilized Brie cheese was used. Transcriptional responses, assessed by RT-qPCR on a panel of selected genes, revealed a temperature-dependent related response. Exposure to Ef–ECP in a cheese-like matrix significantly downregulated key invasion (inlA, inlB, inlC), virulence (plcA, plcB, iap, prfA, sigB), quorum sensing (agrA, agrD), motility (flaA, actA), and acid tolerance (gadD) genes, with a stronger repressive effect at 37 °C than at 7 °C. Although Ef–ECP reduces L. monocytogenes pathogenic potential in a temperature-dependent manner, the persistence of gene activity at 7 °C highlights the residual risk in refrigerated ready-to-eat dairy products and the need for multi-hurdle preservation strategies. Overall, Ef–ECP greatly impaired L. monocytogenes physiology, combining antimicrobial, anti-biofilm, and transcriptional repression effects. Our approach based on postbiotics offers practical advantages for a focused application in food systems, potentially enhancing industrial applicability.