Isolation and identification of tyramine-producing enterococci from human fecal samples

Lactic acid bacteria (LAB) are recognized as a group of important microorganisms because of their crucial role in food fermentation and their contribution to the maintenance of health homeostasis, as natural inhabitants of the human mucosa. However, the metabolic activities of some strains, such as the ability to synthesize biogenic amines (BAs), can be detrimental to human health. BAs are low molecular weight compounds synthesized by the enzymatic decarboxylation of amino acids. Tyramine, one of the most biologically active BAs, is produced by certain strains of LAB related to food fermentations. Since no data are available as to whether tyramine originates exclusively from food intake, or, like polyamines, could be formed by gut bacteria, this study was focused on the isolation of tyramine-producing LAB from human feces. Different strains of Enterococcus faecium and Enterococcus faecalis able to produce tyramine in culture conditions were isolated.