Prevalence, Antimicrobial Resistance and Serotype Distribution of Listeria monocytogenes Isolated from Raw Milk and Dairy Products

The objectives of study were to assess presence of Listeria monocytogenes, perform serotyping and investigate antibiotic resistance in raw milk and dairy products. A total of 210 milk and dairy products including white (n=20) and kashar cheese (n=20), ice cream (n=20), butter (n=20), cokelek (n=10), kuymak (n=10) and farm cheese (n=10) were obtained from Samsun, Turkey. All samples were analyzed using an immunomagnetic separation-based culture technique and strains of L.monocytogenes were confirmed by presence of hlyA and iap genes by polymerase chain reaction (PCR). L.monocytogenes was identified in 5 of 100 (5%) milk samples, serotyped as 4b and 1/2b, and in 9 of 110 (8.2%) dairy products, serotyped as 1/2a, 1/2b and 1/2c. However, L.monocytogenes was not identified from butter, kashar and ice cream samples. The antibiotic susceptibility against ampicillin, amoxicillin/clavulanic acid, erythromycin, chloramphenicol, penicillin G, oxytetracycline, tetracycline and vancomycin was assessed by disc diffusion method. It was found that 15.3% of isolates were resistant to at least one drug and 36.5% were multidrug resistant. Among isolates, resistance to tetracycline was most commonly encountered (34.6%), followed by resistance to chloramphenicol (25%) and penicillin G (23%). In conclusion, our data also indicate that consuming raw and unpasteurised milk and dairy products could pose a risk of listeriosis in humans. Practical ApplicationsAlthough there are plenty of studies about the incidence of L.monocytogenes in raw milk and dairy products in Turkey, our study is the first one in Samsun (Middle Black Sea) Region about Listeria in milk and dairy products. Also in our study, we characterized some virulence genes and serotype distribution of L.monocytogenes by PCR. Finally, we performed antibiotic resistance tests of isolates to see possible public health threats because of using overabundant antibiotics. If we analyze all these work to see the potential risk assessments in this region, our study could be a leading study in near future.