Reduction of Listeria monocytogenes on the Surface of Fresh Channel Catfish Fillets by Bacteriophage Listex P100

Bacteriophage Listex P100 (phage P100) was approved by the U.S. Food and Drug Administration and U.S. Department of Agriculture's Food Safety and Inspection Service for Listeria monocytogenes control on both raw and ready-to-eat food products. In this article, we present the proof of concept on the influence of phage dose, phage contact time, and storage temperature on the listericidal activity of phage P100 in reducing the L. monocytogenes loads on the surface of fresh channel catfish fillet. The fresh catfish fillet samples were surface inoculated with ∼4.3 log₁₀ colony forming units (CFU)/g of a two serotype mix (1/2a and 4b) of L. monocytogenes cells and then surface treated with phage P100. L. monocytogenes reduction was influenced by phage contact time and phage dose regardless of higher or lower temperature regimes tested on catfish fillet. The reduction in L. monocytogenes loads (p < 0.05) with the phage P100 dose of 2 × 10⁷ plaque forming units (PFU)/g (7.3 log₁₀ PFU/g) was 1.4–2.0 log₁₀ CFU/g at 4°C, 1.7–2.1 log₁₀ CFU/g at 10°C, and 1.6–2.3 log₁₀ CFU/g at room temperature (22°C) on raw catfish fillet. The phage contact time of 30 min was adequate to yield greater than 1 log₁₀ CFU/g reduction in L. monocytogenes, whereas 15 min contact time with phage yielded less than 1 log₁₀ CFU/g reduction in L. monocytogenes loads on catfish fillet. Phage P100 titer was stable on catfish fillet samples, and overall reductions in L. monocytogenes counts were still maintained over a 10-day shelf life at 4°C or 10°C by phage P100 treatment. These findings illustrate the effectiveness of an alternative generally recognized as safe antimicrobial such as bacteriophage Listex P100 in quantitatively reducing L. monocytogenes from fresh catfish fillet surfaces.