A survey of Listeria monocytogenes and its virulence factors in vegetable salads and fresh vegetables in Tehran, Iran

Fruits and vegetables have high potential of contamination with pathogenic organisms such as Listeria monocytogenes. Illnesses and outbreaks due to consumption of contaminated fresh products have been increased in recent years. So the aim of this study was to investigate Listeria monocytogenes in vegetable salads and fresh vegetables. Identification carried out using culture method according to Food and Drug Administration (FDA) protocol. PCR assay also used to confirmation of isolates as well as recognition of Hly and acta virulence factors. One hundred vegetable salads and 100 fresh vegetables obtained from three regions under supervision of Tehran University of Medical Sciences, including Islamshahr, Shahr-e-Rey and south of Tehran city. Culture method identified 24% Listeria and 0.5% L. monocytogenes in 200 samples. Confirmation of isolates with PCR resulted in 12% Listeria and 0.5% L. monocytogenes. The only L. monocytogenes was obtained from a ready to eat (RTE) mixed leafy vegetable. PCR assay also recognized presence of Hly and actA virulence factors in isolated L. monocytogenes. The isolated L. monocytogenes was resistant to Ampicillin, Oxacillin and Chloramphenicol, susceptible to Gentamicin, Penicillin G, Erythromycin, Tetracycline, Vancomycin and Trimethoprim sulfamethoxazole and moderate resistant to Methicillin and Doxycycline. Furthermore, poor microbial quality of studied samples was revealed in terms of total microbial count, Enterococcus count and Escherichia coli contamination. Microbial quality assays were based on Iran national standards. About 76.5% of 200 samples exceeded allowed limits in at least one of three mentioned parameters.