listeria monocytogenes isolated from ready-to-eat food products in tehran: prevalence and antimicrobial resistance

L. monocytogenes is a significant foodborne pathogen that is associated with clinical illnesses ranging from self-limited gastroenteritis to invasive infection leading to hospitalization of immunocompromised people. thus, in the current study, the incidence of this bacteria was measured in the rte food of tehran, iran.110 samples were collected from ready-to-eat (rte) foods from different zones of tehran from april until september 2022. the samples were from caesar salad, olivier salad, burger, schnitzel, sushi, and sausage. isolates were identified by detecting hlya and prfa genes applying pcr i.e., polymerase chain reaction. the antimicrobial resistance profile of isolates was assessed through disc diffusion assay and pcr amplification of resistance genes. fourteen among 110 samples (12.7%) were known to be listeria spp. and six samples (5.5%) were l. monocytogenes. using molecular methods. schnitzel and burgers had the highest rate of listeria spp. with 30% of schnitzel and 25% of burger samples. among 14 isolates, 6 samples (42%) were characterized as l. monocytogenes burgers showed the highest rate of l. monocytogenes which was 20% of total burger samples; caesar salad, sausage, and sushi samples contained no identified l. monocytogenes.the isolated l. monocytogenes show resistance against oxacillin, streptomycin, cotrimoxazole, clindamycin, and cefoxitin and are susceptible to chloramphenicol. isolates were semi-susceptible to fosfomycin and ampicillin. the isolates resistant to erythromycin contain genes involved in resistance to the macrolide class of antibiotics (erma and ermb). cfxa and meca genes were only detected in one of the isolates resistant to cefoxitin and oxacillin. overall, there is considerable concern about listeriosis threatening ready-to-eat (rte) food consumers.