Bacteriophage significantly reduces Listeria monocytogenes on raw salmon fillet tissue

We have demonstrated the antilisterial activity of generally recognized as safe (GRAS) bacteriophage LISTEX P100 (phage P100) on the surface of raw salmon fillet tissue against Listeria monocytogenes serotypes 1/2a and 4b. In a broth model system, phage P100 completely inhibited L. monocytogenes growth at 4 degrees Celsius for 12 days, at 10 degrees Celsius for 8 days, and at 30 degrees Celsius for 4 days, at all three phage concentrations of 10(4), 10(6), and 10(8) PFU/ml. On raw salmon fillet tissue, a higher phage concentration of 10(8) PFU/g was required to yield 1.8-, 2.5-, and 3.5-log CFU/g reductions of L. monocytogenes from its initial loads of 2, 3, and 4.5 log CFU/g at 4 or 22 degrees Celsius. Over the 10 days of storage at 4 degrees Celsius, L. monocytogenes growth was inhibited by phage P100 on the raw salmon fillet tissue to as low as 0.3 log CFU/g versus normal growth of 2.6 log CFU/g in the absence of phage. Phage P100 remained stable on the raw salmon fillet tissue over a 10-day storage period, with only a marginal loss of 0.6 log PFU/g from an initial phage treatment of 8 log PFU/g. These findings illustrate that the GRAS bacteriophage LISTEX P100 is listericidal on raw salmon fillets and is useful in quantitatively reducing L. monocytogenes.