Abstract

The anti-listerial activity of generally recognized as safe (GRAS) bacteriophage Listex P100 (phage P100) was demonstrated in broths and on the surface of slices of dry-cured ham against 5 strains or serotypes (i.e., Scott A, 1/2a, 1/2b, and 4b) of Listeria monocytogenes. In a broth model system, phage P100 at a concentration equal to or greater than 7 log PFU/mL completely inhibited 2 log CFU/cm2 or 3 log CFU/cm2 of L. monocytogenes growth at 30 °C. The temperature (4, 10, 20 °C) seemed to influence P100 activity; the best results were obtained at 4 °C. On dry-cured ham slices, a P100 concentration ranging from 5 to 8 log PFU/cm2 was required to obtain a significant reduction in L. monocytogenes. At 4, 10, and 20 °C, an inoculum of 8 log PFU/cm2 was required to completely eliminate 2 log L. monocytogenes/cm2 and to reach the absence in 25 g product according to USA food law. Conversely, it was impossible to completely eradicate L. monocytogenes with an inoculum of approximately of 3.0 and 4.0 log CFU/cm2 and with a P100 inoculum ranging from 1 to 7 log PFU/cm2. P100 remained stable on dry-cured ham slices over a 14-day storage period, with only a marginal loss of 0.2 log PFU/cm2 from an initial phage treatment of approximately 8 log PFU/cm2. Moreover, phage P100 eliminated free L. monocytogenes cells and biofilms on the machinery surfaces used for dry-cured ham production. These findings demonstrate that the GRAS bacteriophage Listex P100 at level of 8 log PFU/cm2 is listericidal and useful for reducing the L. monocytogenes concentration or eradicating the bacteria from dry-cured ham.

Highlights

  • Listeria monocytogenes is an opportunistic pathogenic microorganism that is often implicated in food-borne diseases

  • No growth of L. monocytogenes was observed regardless of the bacterial was dependent on the Phage 100 (P100) concentration, the L. monocytogenes inoculum concentration and the concentration

  • This study showed a high listericidal activity of the P100 on dry-cured ham against 5 different strains or serotypes of L. monocytogenes

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Summary

Introduction

Listeria monocytogenes is an opportunistic pathogenic microorganism that is often implicated in food-borne diseases. The resulting disease can be invasive (bacteremia and meningitis) or non-invasive (gastroenteritis accompanied by fever and vomiting) [1]. L. monocytogenes is a ubiquitous microorganism and can be found in many food products, such as vegetables and vegetable products, milk and dairy products, and meat and meat products [2,3,4,5,6]. Foods with water activity (Aw) less than 0.92 and acidic pH (< 4.0) do not support its growth. The bacteria may still be present in many processed products, those that do not provide thermal treatment post-packaging. The use of the Hazard Analysis Critical

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