Psychrophilic phage phiGM22-3 efficiently controls Pseudomonas fluorescens contamination in cold-stored milk.

Pseudomonas fluorescens is a common spoilage causing microbe found in milk. Antibiotic preservatives may cause emergence of multidrug resistance, posing food safety related risks to public health. Phage treatment may be used as an alternative to antibiotics in controlling P. fluorescens contaminations. Here we reported that P. fluorescens phage phiGM22-3 reproduced rapidly over a broad temperature range of 4 through 30°C, and the optimum growth of phiGM22-3 occurred at 10°C, indicating that it was a psychrophilic virus. Genome analysis revealed that phiGM22-3 has a genome of 42,662 bp with an identical terminal direct repeat sequence of 328 bp and encodes 58 predicted proteins. Evidence revealed that phiGM22-3 recognized lipopolysaccharides (LPS) as receptor for infection. Additionally, two phage mutants phiMX2 and phiMX8 with different host ranges were identified in the phiGM22-3 population. Phage killing efficiency of P. fluorescens cells artificially inoculated in milk was evaluated. Phage phiGM22-3 and the cocktails containing phiMX2 and phiMX8 can lyse almost 100% bacterial cells at 4°C within 24 h. Taken together, our data indicated that the psychrophilic virus phiGM22-3 and its two mutants can efficiently inhibit bacteria growth at 4°C, showing a great potential to be used as alternatives to conventional antibiotics against P. fluorescens in refrigerated foods.