Stress Exposure of Evolved Bacteriophages under Laboratory versus Food Processing Conditions Highlights Challenges in Translatability

Bacterial viruses, or bacteriophages, are highly potent, target-specific antimicrobials. Bacteriophages can be safely applied along the food production chain to aid control of foodborne pathogens. However, bacteriophages are often sensitive to the environments encountered in food matrices and under processing conditions, thus limiting their applicability. We sought to address this challenge by exposing commercially available Listeria monocytogenes bacteriophage, P100, to three stress conditions: desiccation, elevated temperature, and low pH, to select for stress-resistant bacteriophages. The stressed bacteriophage populations lost up to 5.1 log(10) in infectivity; however, the surviving subpopulation retained their stress-resistant phenotype through five passages with a maximum of 2.0 log(10) loss in infectivity when exposed to the same stressor. Sequencing identified key mutation regions but did not reveal a clear mechanism of resistance. The stress-selected bacteriophage populations effectively suppressed L. monocytogenes growth at a modest multiplicity of infection of 0.35-0.43, indicating no trade-off in lytic ability in return for improved survivability. The stressed subpopulations were tested for survival on food grade stainless steel, during milk pasteurization, and within acidic beverages. Interestingly, air drying on stainless steel and pasteurization in milk led to significantly less stress and titer loss in bacteriophage compared to similar stress under model lab conditions. This led to a diminished benefit for stress-selection, thus highlighting a major challenge in real-life translatability of bacteriophage adaptational evolution.

Automated summary

Bacterial viruses, known as bacteriophages, are effective antimicrobials that specifically target bacteria. They can be used safely throughout the food production process to control foodborne pathogens. However, their applicability is limited due to their sensitivity towards the environments found in food matrices and processing conditions. This study aimed to address this issue by exposing a commercially available Listeria monocytogenes bacteriophage, P100, to various stress conditions to select for stress-resistant bacteriophages. The stress-selected bacteriophages showed reduced infectivity but retained their stress-resistant phenotype even after multiple passages. The study also highlighted the challenges in translating bacteriophage adaptational evolution to real-life conditions.