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Cold-smoked salmon treated with divergicin M35-producing Carnobacterium divergens M35, C. divergens ATCC 35677 (a non-producer of bacteriocin), purified divergicin M35 or supernatants of C. divergens M35 culture in snow crab hepatopancreas (SCH) medium or MRS broth was challenged with Listeria monocytogenes (up to 10(3) CFU/g). Samples were stored at 4 degrees C for up to four weeks. L. monocytogenes, total bacterial and lactic acid bacterial counts were determined along with changes in total volatile base nitrogen (TVBN) and biogenic amine production as well as texture, color and odor. A 2.6 log CFU/g reduction in L. monocytogenes was obtained for up to 10 days of storage in samples treated with C. divergens M35. Purified divergicin M35 (50 microg/g), SCH supernatant or MRS supernatant brought reductions of 1 log CFU/g at the beginning of storage. However, the anti-listerial activity of the supernatants lasted for 15 days compared to 3 days for purified divergicin M35. Color and texture were affected little in samples containing C. divergens M35 compared to un-inoculated samples. TVBN and biogenic amine production, particularly tyramine, remained below the maximum acceptable level in fish appreciation. These results clearly show the potential of C. divergens M35 culture as well as divergicin M35 bio-ingredient for application to the inactivation of L. monocytogenes in ready-to-eat seafood.

Three bacteriocin-producing bifidobacterial isolates from newborns were identified as Bifidobacterium thermacidophilum (two strains) and B. thermophilum (one strain). This study was undertaken to evaluate the ability of these strains to compete with food-borne Listeria monocytogenes for adhesion and invasion sites on Caco-2 and HT-29 cells. The bifidobacteria adhered at levels ranging from 4% to 10% of the CFU added, but none of the bifidobacteria were able to invade cells. The abilities of Listeria to adhere to and to invade cells varied widely depending on the strain tested. Three groups of Listeria were identified based on invasiveness: weakly invasive, moderately invasive, and highly invasive strains. One strain from each group was tested in competition with bifidobacteria. B. thermacidophilum RBL70 was the most effective in blocking invasion of Listeria, and the decreases in invasion ranged from 38% to 90%. For all three bifidobacterial strains, contact between the cell monolayer and the bifidobacteria for 1 h before exposure to Listeria increased the degree of inhibition. Finally, visualization of competition for adhesion sites on cells by fluorescent in situ hybridization suggested that the two bacteria tended to adhere in close proximity.

Aims: This study aimed to characterize new isolates of human bifidobacteria, evaluate some of their probiotic potential and to screen these isolates for their effectiveness at inhibiting Listeria monocytogenes in vitro., Methods and Results: Thirty-four Bifidobacterium isolates from infant faeces were identified by fructose-6-phosphate phosphoketolase and PCR. Six isolates, coded RBL67, RBL68, RBL69, RBL70, RBL85 and RBL86, showed higher antagonistic activity against L. monocytogenes. Neutralized culture supernatants of these strains did not inhibit L. monocytogenes when tested by agar diffusion method. However, the concentration of supernatant by speed-vac resulted in the formation of an inhibitory effect with supernatants from strains RBL67, RBL68 and RBL70. This effect was shown to be related to heat-stable proteinaceous compound(s) which were resistant to heating at 100 degrees C for 5 min but not to pronase-E, proteinase-K or trypsin. The extraction of the inhibitory compounds by methanol-acetone extraction procedure indicated that four strains (RBL67, RBL68, RBL69 and RBL70) were mostly soluble in acetone. However, strain RBL85 produced inhibitory substances that were soluble in methanol., Conclusion: Infant bifidobacterial isolates produce heat-stable proteinaceous compounds active against L. monocytogenes., Significance and Impact of the Study: Production of antibacterial substances by bifidobacteria would improve intestinal bacterial ecology and inhibit intestinal pathogens.