Presence and antibiotic resistance of listeria monocytogenes in raw milk and dairy products

In this study, the presence of Listeria monocytogenes in raw milk and milk products produced from raw milk by traditional method, such as cheese and butter using cultural and molecular techniques and the antibiotic resistances were investigated. Isolation was performed using the FDA technique. Microbact 12L test kit was used for biochemical identification. Genotyping of isolates was done by traditional PCR method. Antibiotic resistance of isolates was determined by standard disk diffusion method. Listeria spp. was detected in 16 (5.3%) of the total 300 food samples according to the biochemical identification results. The highest prevalence of Listeria spp. was in raw milk samples (10%), followed by cheese samples (4%) and butter samples (2%). All 36 Listeria spp. isolates which were obtained from biochemical identification were tested for L. monocytogenes by PCR, and 15 (41.6%) of them were confirmed as L. monocytogenes. According to the antibiotic resistance test results of L. monocytogenes strains, four (26.7%) isolates were resistant to at least one antibiotic while only one (6.7%) had multiple antibiotic resistance. The highest resistance was found against trimethoprim-sulfamethoxazole. It has been determined that L. monocytogenes isolates had the same degree resistance against penicillin G, meropenem, amikacin and vancomycin. In conclusion, the presence of L. monocytogenes which has been detected in dairy products made from raw milk and in raw milk itself may constitute a potential risk for public health. Furthermore, it is threatening for public health that the isolates obtained are resistant to certain antibiotics.