Monitoring probiotic properties and safety evaluation of antilisterial Enterococcus faecium strains with cholesterol-lowering potential from raw Cow's milk

Enterococci are an important member of lactic acid bacteria due to their presence in fermented foods, tolerance to low pH and bile salts, bile salt hydrolase (BSH) activity, reducing cholesterol, and producing bacteriocin. However, probiotic and safety issues of enterococci are still debated. It is important to investigate probiotic properties and safety evaluation of these genus because they are intentionally or unintentionally present in foods. In this study, probiotic properties (tolerance to bile salts and simulated gastric juice, antimicrobial and BSH activity, cholesterol lowering potential, auto/co-aggregation, and cell surface hydrophobicity) and safety evaluation (antibiotic resistance, virulence factor, haemolysis and DNase activity, Galleria mellonella infection model, gelatinase activity, and biofilm formation) of Enterococcus faecium (E. faecium) BH04, BH12, BH84, and BH99 isolated raw cow's milk were determined. All strains had high tolerance to bile salts (47.70%–103.84%) and simulated gastric juice (76.80%–82.05%), and antimicrobial activity on L. monocytogenes ATCC 7644 by protein-like substances such as bacteriocin. The strains had strong BSH property and reduced cholesterol by 69.47%–95.00%. The strains were resistant only to gentamicin, kanamycin, and streptomycin and did not have haemolysis and DNase activity. Only gelE and esp genes were detected in some strains. According to the results, it is thought that the E. faecium strains could be possible probiotic candidates. Moreover, this study is the first report on Enterococcus faecium strains isolated from raw cow's milk, which tolerate to bile salt and simulated gastric juice, have BSH potential and antimicrobial activity by protein-like substances, and reduce cholesterol level.