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

## TL;DR

This study examines Enterococcus faecalis strains from raw milk to assess their genetic diversity and ability to produce biogenic amines, which can affect dairy product safety.

## Contribution

The study introduces optimized molecular methods for detecting tyrDC gene presence and its correlation with biogenic amine production in E. faecalis.

## Key findings

- High variability was observed among E. faecalis strains in terms of genetic diversity and biogenic amine production.
- Some isolates produced high concentrations of tyrDC (over 1000 mg/kg), with gene presence strongly correlated to production levels.
- The presence of regulatory or environmental factors influencing amine production was suggested by low-producing tyrDC-positive strains.

## Abstract

In this study, Enterococcus faecalis 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 (hdcA, tyrS, tyrDC, Odc, ldc) was detected by molecular assays, with the use of optimized primers enabling the detection of tyrDC in strains previously considered negative. The results showed high variability between strains and the ability of some isolates to produce high concentrations of tyrDC (max. > 1000 mg/kg); the presence of the tyrDC gene was strongly correlated with high production, although tyrDC-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.