Selection and evaluation of seafood-borne psychrotrophic lactic acid bacteria as inhibitors of pathogenic and spoilage bacteria.

In this study, inhibitory psychrotrophic lactic acid bacteria were isolated and investigated for future use in biopreservation of seafood products. Screening of 5575 colonies isolated from various seafood products resulted in the selection of 132 colonies presenting inhibitory properties. Among them, 52 isolates had characteristics of LAB and showed growth at 15 degrees C but not at 30 degrees C. The inhibition spectrum of these 52 isolates against 14 target strains (Gram-positive and -negative) showed inhibition of typical seafood spoiling and pathogenic bacteria and enabled the formation of seven interesting clusters. Sequencing of the 16S rRNA gene of a representative isolate from each cluster identified three Leuconostoc gelidum, two Lactococcus piscium, one Lactobacillus fuchuensis and one Carnobacterium alterfunditum. Theses strains did not produce histamine nor tyramine, and showed no particular antibiotic resistance profile. Growth rate as a function of temperature was tested for one L. piscium and one L. gelidum isolate and confirmed their psychrotrophic behavior. One out of seven isolates showed bacteriocin-like activity. The inhibition mechanisms of the other isolates are still unknown but may be due to competition for substrate. Absence of a bacteriocin-like component could be a positive point to gain rapid authorization for food application in France. This collection of LAB is now ready for testing on products.

Psychrotrophic lactic acid bacteria used to improve the safety and quality of vacuum-packaged cooked and peeled tropical shrimp and cold-smoked salmon.

Previously isolated lactic acid bacteria (LAB) from seafood products have been investigated for their capacity to increase the sensory shelf life of vacuum-packaged shrimp and cold-smoked salmon and to inhibit the growth of three pathogenic bacteria. Two different manufactured batches of cooked, peeled, and vacuum-packaged shrimp were inoculated with seven LAB strains separately at an initial level of 5 log CFU g-t, and the spoilage was estimated by sensory analysis after 7 and 28 days of storage at 8 degrees C. Two Leuconostoc gelidum strains greatly extended the shelf life of both batches, two Lactococcus piscium strains had a moderate effect, two bacteria were spoilers (Lactobacillus fuchuensis and Carnobacterium alterfunditum), and the last one (another Leuconostoc gelidum strain) showed highly variable results depending on the batch considered. The four strains showing the best results (two Leuconostoc gelidum and two Lactococcus piscium strains) were selected for the same experiment in cold-smoked salmon. In this product, Lactococcus piscium strains showed better inhibiting capacities, improving the sensory quality significantly at 14 and 28 days of storage. Finally, the inhibiting capacities of two strains (one Leuconostoc gelidum strain and one Lactococcus piscium strain) were tested against three pathogenic bacteria (Vibrio cholerae, Listeria monocytogenes, and Staphylococcus aureus) by challenge tests in shrimp. LAB and pathogenic bacteria were coinoculated in vacuum-packaged shrimp and enumerated during 5 weeks. Lactococcus piscium strain EU2241 was able to reduce significantly the number of Listeria monocytogenes and S. aureus organisms in the product by 2 log throughout the study for Listeria monocytogenes and up to 4 weeks for S. aureus.