Presence of Listeria spp. in fish samples, fish products and sea products

Abstract

Listeria monocytogenes is a bacterium that is pathogenic for man and for most animal species. Listeriosis is a generalized infection that starts after ingestion of the causative agent L. monocytogenes (Finlay, 2001). Food that is not properly thermically processed, long storage of such food, food that is produced in inadequate hygienic food plants, as well as cooked-cooled ready to eat food (RTE) is the ideal medium for listeria multiplication. High risk food originated from fish, fish products and sea products comprised of: molluscs (fresh of frozen shellfish, crustaceans shelled or not), fresh fish (ready to eat without cooking), fish products packed with brine (NaCl<6%), (salted, marinated, fermented, cold smoked and fish in brine), thermically treated fish and crustacean products (pasteurization, cooking, hot smoking, including pre-cooking and panning). In this research, fish samples, fish products and sea products from Serbian markets were examinated such as: fresh fish (cooled), frozen food (fish and sea products - cuttlefish, squid, octopus, shellfish, crustaceans and shrimps), panned products; smoked fish, salted fish, thermally treated fish and fish products, semi-canned fish and canned fish. Microbiological testing has been performed according to internationally prescribed standards ISO 11290-1 (1996) "Microbiology of food and animal feed stuffs - Horizontal method for the detection and enumeration of Listeria monocytogenes". There were 470 samples from fish products and sea products. Presence of Listeria spp was registered in 58 samples (12.34%). Listeria monocytogenes was found in 1.92% samples (9 isolates), which makes 15.52% of the total Listeria that were isolated from the tested food. Other isolated Listeria belong to the following species: L. innocua (8.51%), L.welshimeri (1.28%), L.welshimeri/innocua (0.21%), L. grayi (0.21%) and L. seeligeri (0.21%). Exceptional viability of Listeria monocytogenes in the food tested was documented, also (freezing temperature - 18oC, five months).