Isolation of Listeria monocytogenes from Meat and Dairy Products

Introduction: This study was intended to determine the presence and distribution of Listeria monocytogenes in various meat and dairy products from Qazvin Province by culture followed by biochemical and morphological assays. The identity of the isolates was further obtained by amplification of prfA gene in bacteria isolates. This gene is a transcriptional activator of virulence gene expression within the pathogenic L. monocytogenes. Method: In a cross-sectional design, a total of 182 different food samples were collected from different areas in Qazvin, Iran. Bacterial isolates were obtained by the cold enrichment method. DNA extraction from the pelleted cells was conducted and then prfA gene was amplified by conventional PCR. Results: As many as 37 (20.3%) food samples were positive for Listeria spp. including 21 (56.8%) L. monocytogenes, 7 (18.9%) Listeria innocua, 4 (10.8%) Listeria welshimri, 3 (8.1%), Listeria seligeri, and 2 (5.4%) Listeria grayi. None of the isolated specimen was Listeria ivanovii. The PrfA gene was amplified in all L. monocytogenes specimen. Moreover, PCR assay had high sensitivity and specificity for bacterial identification. Conclusion: To sum up, presence of L. monocytogenes in food samples was confirmed in this region, it was more frequent in milk specimen. In addition to common culture techniques, PCR assay showed higher sensitivity and specificity for L. monocytogenes detection in contaminated foods.