Molecular Identification and Biogenic Amine Production Capacity of Enterococcus faecalis Strains Isolated from Raw Milk

In this study, <i>Enterococcus faecalis</i> strains isolated from raw cow's milk were examined for genetic diversity, ability to produce biogenic amines (including histamine, tyramine, putrescine, cadaverine, 2-phenylethylamine) and the presence of corresponding amino acid decarboxylase genes. Identification of 29 strains obtained from Polish farms was carried out by polymerase chain reaction (PCR) and matrix-assisted laser desorption and ionization time of flight (MALDI-TOF MS) methods, and their genetic relationships were assessed by the Enterobacterial Repetitive Intergenic Consensus Polymerase Chain Reaction (ERIC-PCR) technique. Amine production capacity was assessed in vitro on synthetic medium, while the presence of decarboxylase genes (<i>hdcA</i>, <i>tyrS</i>, <i>tyrDC</i>, <i>Odc</i>, <i>ldc</i>) was detected by molecular assays, with the use of optimized primers enabling the detection of <i>tyrDC</i> in strains previously considered negative. The results showed high variability between strains and the ability of some isolates to produce high concentrations of <i>tyrDC</i> (max. > 1000 mg/kg); the presence of the <i>tyrDC</i> gene was strongly correlated with high production, although <i>tyrDC</i>-positive strains with low production were also reported, suggesting the influence of regulatory or environmental factors. The study underscores the need for precise molecular tools and systematic monitoring of biogenic amines to ensure the safety and quality of dairy products.