Research

Antilisterial Carnobacterium Species from Processed Fish

Problem: The Alaska seafood industry is interested in projects that will reduce the presence of Listeria monocytogenes in products as one of the seafood safety issues listed at the ComFish Alaska meeting last year. Use of probiotic bacteria such as the carnobacteria would fall under the headings of new product technologies and byproducts of seafood processing.

Approach: Probiotic bacteria are present in nature and are beginning to be discovered in marine fish. These beneficial bacteria may be the next generation of food preservation tools against food pathogens. This project will explore the prevalence of Carnobacterium species among the lactic acid bacteria that may be found in commercially-harvested Alaskan fish. Selected strains will be tested against a surrogate (Listeria innocua) for the pathogen L. monocytogenes in cold-smoked salmon. The goal of this project is to discover new strains of antilisterial bacteria from Alaska fish that will be useful in developing safer ready-to-eat products. Our specific objectives included ascertaining the prevalence of antilisterial bacteria in the intestinal tract and gills from commercially harvested Alaska fish. We will isolate these and taxonomically confirm the identity of the isolates. We will determine the potency of bacteriocins produced by the presumptive antilisterial bacteria.

Results: Population levels of carnobacteria, from the intestines and gills of commercially-harvested Alaskan fish, were less than 1,000 per gram. Several isolates of Carnobacterium species have been successfully isolated from the intestines of sockeye salmon and the gills and intestines of Pacific herring. Taxonomic identification through the MicroLog 2 system (Biolog) confirmed these to be C. piscicola, C. divergens and C. mobile. Bacteriocin analysis of cell supernatants showed a wide range of inhibition zones and levels of activity units against the non-pathogen Listeria innocua, a surrogate for the pathogen L. monocytogenes.The top four bacteriocin-producing strains and two culture stocks from the FITC collection were found to produce higher levels of bacteriocin than four strains obtained from the American Type Culture Collection. Cross-reactivity experiments demonstrated the new isolates had different patterns of inhibition against like and similar species. Bacteriocins produced in this study, while effective in inactivating L. innocua under lab conditions, were not successful under processing plant conditions for salmon lox. The probiotic cultures may be more effective if combined with standard food-grade inhibitory additives.

Presentations & Publications: None

Contact person: Dr. Brian Himelbloom email: bhhimelbloom@alaska.edu