Investigation of the presence of Listeria monocytogenes in minced meat samples sold in Istanbul province

Genus Listeria are Gram positive, non-spore-forming and facultative anaerop microorganisms which can be found in a wide variety of environments such as soil, feces, water, waste water, plants, nutrients, human, animal and animal feed. Among the 21 different species of the Listeria genus, Listeria monocytogenes is the most common and listeriosis agent in humans. Meat and meat products have a very important role in foodborne infections. L. monocytogenes has a high mortality rate among all foodborne infections, and this mortality rate is higher than the mortality rates of other common foodborne pathogens such as Salmonella Enteritidis, Campylobacter and Vibrio species. In this context, in our thesis, it is aimed to determine the presence of L. monocytogenes bacteria, which are dangerous for public health, in minced meat samples sold in Istanbul province. In this study, 100 minced meat samples purchased from different butchers in 11 districts of Istanbul between December 2018 and November 2019 were examined for the presence of L. monocytogenes. In our study, the culture method of the United States Department of Agriculture-Food Safety and Inspection Service (USDA-FSIS) was used for the isolation of L. monocytogenes, from the minced meat samples. Antibiotic resistance profiles of bacteria isolated by traditional culture method and identified as L. monocytogenes through biochemical tests were determined by disc diffusion method using 13 different antibiotics. The bacteria identified as L. monocytogenes through biochemical tests were also molecularly verificated according to the presence of iap and hlyA gene regions by the polimerase chain reaction (PCR) method As a result of biochemical tests, it was determined that 21 of 186 suspect isolates obtained by classical culture methods were L. monocytogenes. When antibiotic susceptibility tests of 21 strains identified as L. monocytogenes are evaluated, it was found to be resistant to Amoxicillin/Clavulanic acid (14.28%), penicillin (9.52%), cefaclor (9.52%), vancomycin (9.52%), ciprofloxacin (9.52%) and trimethoprim-sulfamethoxazole (9.52%) and susceptible to ampicillin (100%) and to tetracycline (100%). When 21 isolates, isolated by classical culture method and identified as L. monocytogenes as a result of biochemical tests, were examined in terms of iap and hlyA gene regions, only 16 were found to be L. monocytogenes. The 16S rRNA sequences obtained from the sequence analysis of 16 strains confirmed as L. monocytogenes were identified based on the GenBank database with the NCBI BLAST program. According to the data obtained, it was insufficient to make the diagnosis of L. monocytogenes by using only the traditional culture method and biochemical test, it should be also supported by molecular methods. In our study with minced meat offered for sale in Istanbul, although, the L. monocytogenes isolation rate (17%) and the incidence of antibiotic resistance of the isolated L. monocytogenes bacteria are low, it was concluded that minced meat may pose a public health risk, since L. monocytogenes bacteria are not allowed in foods. It is recommended to frequently examine the samples such as minced meat that can be consumed without heat treatment or that may cause cross-contamination in the kitchen environment, for this bacteria and to pay attention to hygiene and sanitation practices in slaughterhouses and butchers.