Detection of listeria monocytogenes in raw milk and ready to eat dairy products with evaluating the antimicrobial effect of cold-pressed nigella sativa oil

Abstract EN

The objectives of this study were to evaluate the public health significance of Listeria monocytogenes in milk and some dairy products and to estimate the antimicrobial effect of Nigella sativa oil on artificially contaminated soft Damietta cheese.

The highest prevalence rate of L.

monocytogenes was detected in goat milk (26.7 %) followed by buffalo milk & yoghurt (13.3 % each) then kareish cheese (10 %) and finally sheep milk samples (6.7 %).

CHROMagar ListeriaTMTM medium performed better than Oxford agar medium in detection of L.

monocytogenes.

Out of the 90 samples tested, 21/90 (23.3 %) and 13/90 (14.4 %) were presumptively positive for Listeria spp.

on Oxford agar and CHROMagar ListeriaTM media, respectively.

Further biochemical identification of the suspect colonies on Oxford agar and the chromogenic medium revealed that 5/21 (23.8%) and 12/13 (92.3%) of the isolated organisms, respectively were confirmed as L.

monocytogenes.

by applying PCR technique for detection of listeriolysin (hly A) gene, 3/90 (3.3 %) of the total examined samples and 3 / 12 (25 %) of biochemically confirmed isolates were positive (gave specific 750 bp band).

A trial was made to control L.

monocytogenes contamination in Damietta cheese by using cold-pressed Nigella sativa oil.

The results revealed a progressive highly significant reduction in the logarithmic count of L.

monocytogenes (P ≤ 0.01) in the sample treated with this oil.