Detection of the contamination sources of Listeria monocytogenes in pickled white cheese production process line and genotyping with the pulsed-field gel electrophoresis method
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This study was conducted to determine the contamination sources, serotyping profiles, and antibiotic resistance patterns of Listeria monocytogenes isolated during the production of pickled white cheese. The genetic-relatedness of the isolates to EGD SLCC (5835) (1/2a, lineage II) and ATCC (13932) (4b, lineage I) reference strains was also determined with pulsed-field gel electrophoresis (PFGE) as a result of digestions with AscI and ApaI enzymes. Samples were collected from 16 different points in the production process of 4 different plants at 3 different times. Among the 192 samples examined, 17 (8.85%) were determined to be contaminated with Listeria spp. Three isolates (3.53%) obtained from raw milk, wall/ground, and press cases were identified as L. monocytogenes via the conventional culture method and confirmed by polymerase chain reaction. These isolates were found to belong to serotype 4b. According to antibiotic resistance testing against 10 antibiotics (ampicillin, gentamicin, erythromycin, tetracycline, chloramphenicol, cefalotin, streptomycin, vancomycin, penicillin, and sulfamethoxazole/trimethoprim), it was determined that isolates from raw milk and press cases were resistant to erythromycin. PPGE band patterns of the isolates displayed indistinguishable with AscI and 80%-94% homology with ApaI. The isolates were observed to display high homology to ATCC (13932) and lower homology to EGD SLCC (5835) obtained by both enzymes.