Background: Listeria monocytogenes (L. monocytogenes) is a serious zoonotic and food transmitted human pathogen causing meningitis and abortions. Several outbreaks of listeriosis have been associated with consumption of ready-to-eat food (RTE) products including dairy, meat, and fish and contaminated fruits and vegetables all over the world.
Aim: This study was designed to detect and characterize L. monocytogenes isolated from local and imported fish in Jordan.
Methods: A total of 170 (70 local and 100 imported; 140 fresh and 30 frozen) fish samples were used in the study. L. monocytogenes was cultured and initially identified using routine microbiological methods. Confirmation and serotyping were performed using PCR. The in vivo pathogenicity and LD50 of isolated L. monocytogenes were determined by oral and intraperitoneal administration in mice. Results: A total of 72 Listeria spp. isolates were cultured from fish. Of those, 24 were positively identified as L. monocytogenes. Other strains of Listeria spp. were L. ivanovii (21), L. innocua (11) and L. grayi (16). Serotyping of the L. monocytogenes indicated that 14 isolates were belonging to the 1/2b, 3b serotypes whereas 10 isolates were belonging to the 4a and 4c serotypes. All isolates were virulent to mice with an LD50 dose ranging from 3 x1010 cfu/ml to 3 x 107.5 cfu/ml. All of the virulent isolates belonged to the serotype 1/2b. Histopathologically, dead mice showed multiple necrotic lesions in the liver and spleen.
Conclusion: Results of this study showed the presence of potentially pathogenic L. monocytogenes in fresh and frozen, local and imported fish in Jordan. Strict monitoring and quality control regulatory measures must be adopted to prevent future outbreaks of food poisoning associated with fish consumption.
Key words: L. monocytogenes, Fish, Serotypes, virulence, Nested PCR
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