Antilisterial potential of bacteriocinogenic Lactobacillus plantarum L001 and Enterococcus faecium L103 isolated from fermented foods

Listeriosis is a severe gastrointestinal disease that affects human health significantly. It is caused by the invasion of Listeria monocytogenes, which secretes virulence factors such as invasion-associated protein (IAP) and listeriolysin O (LLO). Although antibiotics are commonly prescribed for the treatment of listeriosis, overuse can lead to antimicrobial resistance. Lactic acid bacteria (LAB), which produce bioactive metabolites, and exhibit probiotic and antibacterial effects, have been explored as an alternative to antibiotics. In the present work, 83 LAB isolates were screened for 51 bacteriocinogenic-structural genes, and 4.8% of the isolates harboured these genes. Bacteriocinogenic LAB strains were evaluated for their antilisterial activity and mechanism of action against haemolytic L. monocytogenes ATCC19111. The results showed that only Enterococcus faecium L103 and L104, which produce Enterocin L50 (EntL50), showed antilisterial activity in the disc diffusion assay. The mechanism of action of these two strains was determined using HCT-8 cells, in which the exclusion assay was the main inhibition factor contributing to a 50% reduction in the infection assay, and was visualised using field-emission scanning electron microscopy (FESEM). The inhibition of infection was also supported by the absence of p60 protein expression. Heat-inactivated (HI) bacteriocinogenic LAB also conferred immunomodulatory effects by controlling the secretion of TNF-α and CXCL8 from L. monocytogenes infected cells. In conclusion, heat-inactivated LAB can potentially reduce the pathogenicity of L. monocytogenes in vitro, and should be further evaluated in pre-clinical studies.