Qualitative Detection of Biogenic Amine-Producing Bacteria

To detect bacteria producing biogenic amines, a qualitative test was used [43 (link)]. First, strains were inoculated at 1% (v/v) in modified MRS broth containing 0.1% (w/v) of each amino acid precursor (L-lysine, tyrosine disodium salt, L-histidine monohydrochloride and L-ornithine monohydrochloride (Sigma Aldrich, Darmstadt, Germany)) and incubated at 37 °C for 18 h. The screening was carried out using a specially formulated agar medium (0.5% tryptone, 0.5% yeast extract, 0.5% meat extract, 0.25% NaCl, 0.05% glucose, 0.1% Tween 80, 0.02% MgSO₄, 0.005% MnSO₄, 0.004% FeSO₄, 0.2% ammonium citrate, 0.001% thiamine, 0.2% K₂PO₄, 0.01% CaCO₃, 0.005% pyridoxal-5-phosphate, 1% amino acid precursor, 0.006% bromocresol purple, 2% agar; pH 5.3). For this, 10 µL of each culture was spotted on the medium containing the same amino acids precursor. After 4 days of incubation at 37 °C, a positive result was indicated by the color change and by amino acid precipitation around the corresponding spot for tyramine only. The assays were conducted in duplicate.