Prevalence and Antimicrobial Resistance of Listeria monocytogenes in Raw Milk in Tehran, Iran

One of the major sources of Listeria monocytogenes, as the causative agent of invasive listeriosis, is raw milk. The aim of the present study was to detect Listeria monocytogenes in raw milk samples collected from dairy stores in Tehran, Iran, 2019. Material and Methods: A total of 100 raw milk samples were assessed using cultural techniques. Furthermore, antimicrobial resistance profiles of the Listeria isolates were assessed against eight antimicrobials using disc diffusion method. Results and Conclusion: Listeria spp., including Listeria grayi (5%), Listeria ivanovii (3%) and Listeria monocytogenes (2%), were detected in 10% of the samples. Listeria monocytogenes isolates were susceptible to major antimicrobials used for the treatment of listeriosis with no multidrug resistances. The highest frequencies of resistance were seen against streptomycin (60%), gentamicin (50%) and tetracycline (50%). In conclusion, potential risks of listeriosis still threaten consumers of the raw milk in Tehran.