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
Summary
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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