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 lt 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).

Listeria monocytogenes je bakterija patogena za ljude i veliki broj životinjskih vrsta. Listerioza predstavlja generalizovanu infekciju koja nastaje nakon oralne ingestije uzročnog agensa L. monocytogenes (Finlay, 2001). Navedena bakterija se najbolje razvija u namirnicama koje nisu adekvatno termički obrađene; koje su dugo skladištene; koje su proizvedene na mestu na kojem principi higijenskog rukovanja hranom nisu sprovođeni; kuvano-hladnoj hrani spremnoj za jelo (ready to eat food - RTE) U visoko rizične namirnice počev od vrsta ribe, proizvoda od ribe i plodova mora ubrajaju se: mekušci (sveže i zamrznute školjke, rakovi u ljušturama, ili očišćeni), sveža riba (koja se konzumira bez termičke obrade), riblji proizvodi u vodenom rastvoru soli (NaCl%), (soljena, marinirana, fermentisana, hladno dimljena i riba u sopstvenom soku), srednje termički obrađeni riblji proizvodi i rakovi (pasterizacija, kuvanje, toplo dimljenje, uključujući i pred-kuvanje i panirani proizvodi). Kao materijal za ispitivanje korišćeni su uzorci riba, proizvoda od riba i morski plodovi: sveža riba (u rashlađenom stanju), zamrznute namirnice (riba i morski plodovi - lignje, sipe, hobotnice, školjke, rakovi i škampi), panirani proizvodi, dimljena riba, usoljena riba, termički obrađena riba i proizvodi od ribe, polukonzerve i konzerve od ribe. Mikrobiološko ispitivanje je rađeno prema propisanoj metodi po Međunarodnom standardu ISO 11290-1 (1996) 'Microbiology of food and animal feeding stuffs - Horizontal method for the detection and enumeration of Listeria monocytogenes'. Ukupno je ispitano 470 uzoraka ribe, proizvoda od ribe i morskih plodova. Prisustvo Listeria vrsta utvrđeno je u 58 uzoraka (12,34%). Listeria monocytogenes je utvrđena kod 1,92% pregledanih uzoraka (9 izolata) i čini 15,52% od svih vrsta iz roda Listeria koje su izolovane iz navedenih namirnica. Ostale vrste listerija koje su izolovane pripadale su: L. innocua (8,51%), L. welshimeri (1,28%), L. welshimeri/innocua (0,21%), L. grayi (0,21%) i L. seeligeri (0,21%). Ustanovljena je izuzetna sposobnost preživljavanja pri niskim temperaturama vrste Listeria monocytogenes u namirnicama koje su čuvane pri temperaturi od -18oC tokom 5 meseci.