Introduction

Although foodborne infections with the ubiquitous bacterium Listeria (L.) monocytogenes are comparatively rare, they are of great importance due to their severity and high mortality rate which averages at ca. 7%. In addition to the various measures taken to reduce L. monocytogenes during the production of meat products, new methods for lowering bacterial contamination, such as non-thermal high-pressure treatment and biopreservation with bacteriophages, offer an opportunity to further reduce the risk of L. monocytogenes occurring in meat products. Biocontrol strategies with highly effective lytic bacteriophages can also be utilised to control L. monocytogenes.

Goal

Combining L. monocytogenes-specific phages with a mild high-pressure treatment will ensure adequate protection against Listeria. This way, the existing limitations of the respective methods for reducing L. monocytogenes in sausage products can be countered. Here, results of the infection effects of the two commercial phage products used in this study to infect Listeria at temperatures of 7°C are presented. In addition, the impact of food components such as salt, nitrite and spices on phage infection efficiency and Listeria reduction are investigated.

Results

A protocol for extraction of the bacteria and the two phage preparations from the sausage medium was successfully developed and can be used in future experiments. The tested L. monocytogenes strains could grow at both tested temperatures and, as expected, displayed a significantly increased growth rate at 37°C. In addition, the infection efficiency of both phages was also temperature-dependent and the countable plaques were drastically reduced for some strains at 7°C when compared to 37°C. The influence of bacterial growth and phage effectiveness were not noticeably influenced by the food components which included spice mixtures and sodium nitrite. The phage products have good infection efficiency. In combination with the high-pressure process, interesting results will be obtained.

Summary The phage products show a different infection rate at lower temperatures, which is essential information that will impact further treatments.