Bacteriophage Significantly Reduces Listeria monocytogenes on Raw Salmon Fillet Tissue

Abstract

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.

Screening and characterisation of bacteriophage P100 insensitive Listeria monocytogenes isolates in Austrian dairy plants

“…These findings correlate with data of several other studies, where a Listeria reduction by up to five log scales and a concentration dependent effect (less phages or infection of higher bacteria densities were less effective) were described and complete eradication of the pathogen long term or eradication of high bacteria concentrations was not possible (Guenther et al, 2009;Guenther & Loessner, 2011;Silva, Figueiredo, Miranda, & de Castro Almeida, 2014;Soni & Nannapaneni, 2010a, 2010bSoni, Nannapaneni, & Hagens, 2010). The fact that Listex™ P100 is not able to eradicate high concentrations of L. monocytogenes completely may enhance the risk for development of phage insensitive Listeria isolates.…”

Bacteriophage cocktail significantly reduces or eliminates Listeria monocytogenes contamination on lettuce, apples, cheese, smoked salmon and frozen foods

“…While the effect at either application rate was significantly different than the control (p < 0.05 for the lower application rate and p < 0.01for the higher application rate), the higher application rate did not result in a statistically significant decrease in the amount of viable L. monocytogenes compared to the lower application rate. These observations are in general agreement with those reported earlier for raw salmon applications, where phages reduced the levels of L. monocytogenes by 0.8e3.5 log (Guenther et al, 2009;Soni and Nannapaneni, 2010). The better reduction in the L. monocytogenes levels reported by Guenther et al (2009), at a similar inoculum level, could be due to a higher phage application rate of 3 Â 10 8 PFU/g compared to that used in our study, further supporting the idea that the efficacy of phage treatment is phage concentration-dependent (Guenther et al, 2009).…”

Use of epifluorescence microscopy to assess the effectiveness of phage P100 in controlling Listeria monocytogenes biofilms on stainless steel surfaces

“…A reason why bacterial cells were visualized by microscopy but not on agar plates is the fact that the phages were on the plates and therefore lysed the bacterial cells before they grew into colonies. To overcome this disadvantage of cultivation method, some researchers recommend the removal of phages from the sample prior to culture bacteria, in order to determine the bacterial reduction due to the virulent activity of the phages on the samples rather than the infection by free phages present on agar (Sharma et al, 2009;Soni & Nannapaneni, 2010a). However, phage removal does not assure the elimination of all viruses attached to the microorganism, and consequently, a residual activity of the phage will remain in the cultivation method.…”