Molecular characterization and in vivo pathogenicity study of Listeria monocytogenes isolated from fresh and frozen local and imported fish in Jordan

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 the consumption of ready-to-eat food products; dairy, meat, fish, and contaminated fruits and vegetables worldwide. AIM: This study was designed to detect and characterize L. monocytogenes isolated from local and imported fish in Jordan. METHODS: A total of 170 fish (70 local and 100 imported), of which 140 fresh and 30 frozen samples were used in this study. Listeria monocytogenes was cultured and initially identified using conventional microbiological methods. For confirmation and serotyping of the L. monocytogenes isolates, PCR techniques were used. Using oral and intraperitoneal administration, mice were used to determine the pathogenicity and LD(50) of the isolated L. monocytogenes. 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 belonged to the 1/2b, 3b serotypes whereas 10 isolates belonged to the 4a and 4c serotypes. All isolates were virulent to mice with an LD(50) dose ranging from 3 × 10(10 )CFU/ml to 3 × 10(7.5 )CFU/ml. All 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.