Detection of Listeria Species in Minced Beef


Abstract: In recent years there has been an increase in the number of outbreaks of human listeriosis and contaminated foods have been considered to be a potential source of infection. In this study, a total of 100 minced beef samples were obtained from different butchers and supermarkets in Ankara and examined for the presence and degree of contamination with Listeria species. The minced beef samples were collected in aseptic conditions and transported to the laboratory in cold storage. The method suggested by USDA - FSIS was used for the isolation and identification of Listeria spp. In addition, the degree of contamination in Listeria spp. positive samples was determined using the Most Probable Number technique. Different Listeria spp. were isolated from 97% of the 100 samples analysed at the level 0.23 - 2.9 x 10^3 MPN/g. L. innocua was the most prevalent species (92%), followed by L. monocytogenes (28%), L. murrayi (10%), L. grayi (9%), L. seeligeri (3%) and L. welshimeri (2%) . L. ivanovii couldn't be detected in any of the samples. Moreover, according to the analysis, there were mixed sources of contamination, mostly L. innocua and L. monocytogenes. The degree of contamination of L. monocytogenes in the samples was determined to be 0.72 - 2.9 x 10^3 MPN/g. In conclusion, this study has confirmed previous reports that minced beef is one of the major sources of Listeria spp. and particularly that the consumption of uncooked and undercooked minced beef may be a potential danger to the consumer in respect to food-borne diseases.

Keywords: Minced beef, Listeria spp., isolation, identification

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