Effects of bacteriophages on Listeria spp. and listeria biofilm isolated from some foods and food processing facilities and on the biofilm formed by Listeria

Listeria and Listeria biofilm cause foodborne dieases worldwide, primarily in the food industry and public health. In recent years, antibiotics and disinfectants couldn't effective against pathogens and their biofilm structures any more. For this reason, new combat methods such as bacteriophage therapy are being introduced. In this study, a total of 154 samples were screened to investigate the effect of bacteriophages on Listeria spp. and the biofilms they formed. A total of 38 isolates were confirmed as Listeria spp. In this study, 5 of the isolated Listeria spp. and 4 different Listeria reference strains were used. ListexTM P100™ phage, and also FMWLLM3 bacteriophage obtained from the University of Canterbury were used as bacteriophages. Biofilms were formed on microplates and food contact surfaces (steel, galvanized, plastic) with Listeria isolated from the samples. After 9 days of incubation of ListexTM P100 bacteriophage (106 pob/ml concentration) on various surfaces at 37°C, the highest reduction was determined to be 3,96 log on the local isolate L. monocytogenes, while the highest reduction after 9 days of incubation at 25°C was 3,56 log on L. monocytogenes ATCC #13932. After 9 days of incubation at 37°C, the highest reduction of FMWLLM3 bacteriophage (106 pob/ml concentration) was 4,7 log on L. monocytogenes Lm 2000/47. After 9 days of incubation at 25°C, the highest reduction of FMWLLM3 bacteriophage (106 pob/ml concentration) was determined to be 2,88 log on L. monocytogenes Lm 2000/47. This was followed by L. monocytogenes isolate with a 2,50 log decrease. In examinations conducted with SEM microscopy, biofilm formation by Listeria spp. was observed on all tested surfaces (stainless steel, plastic, and galvanized), and the effect of both phages (at a concentration of 106 PFU/ml) on these biofilms was observed. In this study, Listeria bacteriophages were also isolated in 5 different samples (fish body parts, river water, manure, straw and silage). However, successful results were not obtained as a result of phage multiplication processes. This result suggested that the bacteria may have escaped phage integration and protected itself by switching to L form, a situation observed in many gram-positive bacteria.