Isolation, characterization, and application of bacteriophages to reduce and inhibit Listeria monocytogenes in celery and enoki mushroom

Listeria monocytogenes is a foodborne microorganism that causes listeriosis in humans and can even lead to death, especially among older adults, pregnant women, and infants. Ready-to-eat salad is a high-risk food associated with listeriosis in humans because of the minimal processing involved in its preparation. This study aimed to evaluate the efficacy of a bacteriophage cocktail as a biocontrol agent against L. monocytogenes in celery and enoki mushroom. Three lytic phages, named LMPC01, LMPC02, and LMPC03, were isolated from sewage, river, and soil, respectively, and classified as belonging to the Myoviridae (LMPC01 and LMPC02) or Siphoviridae (LMPC03) family by morphology observation. The isolated phages exhibited lytic activity against L. monocytogenes and similar adsorption rates (90% adsorption within 30 min), latent periods (50 min with a burst size of 69.5, 20.3, and 93.0 PFU/CFU, respectively), and survivability (at temperatures between 4 and 50 °C and pH 4–10). In vitro lysis kinetics showed that at a multiplicity-of-infection (MOI) 10 of phage cocktail could consistently inhibit the growth of L. monocytogenes at 30 °C for 24 h. In the time−kill assay, treatment with the phage cocktail (MOI = 10) reduced the L. monocytogenes count by approximately 4.0 log CFU/mL at 4 °C. In the food test, the phage cocktail (MOI = 10) reduced 2.2 and 1.8 log CFU/g of L. monocytogenes contaminated (5.0 log CFU/g) celery and enoki mushroom stored at 4 °C for 7 days. These results highlight that the phage cocktail of LMPC01, LMPC02, and LMPC03 is a potentially promising biocontrol candidate for reducing and inhibiting L. monocytogenes in fresh-cut celery and enoki mushroom.