Investigation of the presence of listeria species from animal-originated food products by conventional and molecular methods

In the transport of Listeria species, food is the primary transport medium for infection; meat and meat products, milk and dairy products, aquatic products and vegetables are the potential sources. The main purpose of this study was to compare the incidence of Listeria species, especially L. monocytogenes, in animal-originated food products, and to develop a new, reliable and rapid method based on Real-Time PCR by shortening the pre-enrichment and selective enrichment times for the detection of Listeria monocytogenes. In the study, it was also aimed to determine the phenotypic and genotypic virulence characteristics of Listeria species isolated from animal-originated food products, and to determine the antibiotic resistance characteristics of the strains. The obtained data showed that 36 of the 200 food samples studied were contaminated with Listeria monocytogenes, 33 with Listeria welshimeri, 24 with Listeria innocua and two with Listeria seeligeri. With the VIDAS UP LISTERIA and ISO 11290-1 methods used in isolation, 35 and 12 L. monocytogenes were isolated, respectively, and it was determined that VIDAS UP LISTERIA method is more selective method in animal-originated food products than ISO 11290-1 method. As a result of serotyping of 36 isolated L. monocytogenes strains; 20 of them 1/2a, 3a; 11 of them were determined as 1/2c, 3c and five of them as 4b, 4d, 4e serotypes. The distribution of virulence genes varied between species. In our study, it was determined that 16 L. monocytogenes isolates were CAMP negative, 31 L. monocytogenes isolates had positive PI-PLC activity, while all L. monocytogenes strains had hemolysis activity. It was determined that the isolated Listeria species were sensitive to 98.94% vancomycin, 88.4% amoxicillin- clavulanic acid, 86.3% gentamicin, 85.2% amikacin, 84.2% ampicillin and 73.7% penicillin G. In the artificial contamination and retrieval study performed with Real-Time PCR, it has been shown that 30 cfu/mL of L. monocytogenes initially inoculated in chicken meat used as a model food, could be detected at the level of 30 cfu/mL after a six-hour pre-enrichment period, thus shortening the isolation period.