Introduction: Foodborne bacterial pathogens can cause significant health and economic impacts worldwide. Listeria (L.) monocytogenes frequently leads to outbreaks and food recalls due to contamination. Bacteriophage (phage) -based products claiming to have broad host ranges against Listeria are commercially available. Although these products are already approved for use in countries like Israel, Canada, China, Switzerland, Australia and New Zealand, they are still awaiting approval in Germany. Goals: The aim of this study is to systematically investigate the efficacy of these phage-based products against sequenced and genotypically distinct clinical (n=20 most common genotypes) and food-associated (n=30) L. monocytogenes strains currently circulating in Germany. We also compared various experimental techniques for the determination of phage susceptibility and evaluated their strengths and weaknesses. Methods: A commercially available phage product against L. monocytogenes was used. The determination of susceptibility of clinical and food-associated L. monocytogenes strains was investigated by spot assays, plaque assays, colony reduction, flow cytometry and optical density measurements (OD₆₀₀). Results: Out of 50 Listeria monocytogenes isolates, 70% and 76% of the strains were found to be susceptible to the phage product in spot and plaque assays, respectively. When using the colony reduction method (n=20), flow cytometry (n=50) and OD₆₀₀ (n=50), phage incubation substantially reduced live cell counts after 24 hours for all isolates compared to the control without phage. With flow cytometry, a substantial reduction could even be seen after 3 hours incubation (Fig. 1). Summary: Preliminary results demonstrate the effectiveness of the phage-based product on currently circulating strains of L. monocytogenes and indicate the biocontrol potential for the reduction of listeriosis should it be approved. It might also be prudent to rethink the use of plaque and spot assays, which are currently considered to be the gold standard for phage susceptibility testing in favor of methods that directly address bacteria reduction, e.g. colony reduction, flow cytometry and OD₆₀₀.