Evaluation of the effects of treatment of Lactococcus lactis and Bifidobacterium bifidum on the expression of biogenic amine-producing genes in Staphylococcus strains isolated from milk

This study investigated the effect of probiotic bacteria Lactococcus lactis and Bifidobacterium bifidum on the expression of the cadaverine and putrescine producing gene in staphylococci species isolated from milk. Staphylococci were identified and isolated from 100 samples of raw milk using standard biochemical methods, Gram staining and 16srRNA sequencing. Samples containing these strains were examined by HPLC for the production of biogenic amines. The presence of the target genes was determined by MultiplexPCR. Bacteria with target gene were treated with Lactococcus lactis supernatant and Bifidobacterium bifidum and the expression of genes was measured by Real time PCR. The data showed that 60 strains of Staphylococcus were isolated, 54 strains of them had target genes. In three samples the level of the cadaverine and putrescine was higher than others. The levels of biogenic amines in the second and third days were significantly higher than the first day (p <0.001). The MIC results obtained for Staphylococcus bacteria exposed to probiotic bacteria in the samples were 125 μg/ml or 62.5 μg/ml. The results of  Real Time PCR reaction showed that the mean reduction in the level of changes in gene expression was statistically significant (p <0.05). This study showed that the use of probiotic bacteria can reduce this bacteria populations and increase the quality of milk by reducing the expression of the biogenic amines-producing genes.