Purpose: The goal of this study is to evaluate antimicrobial strategies using bacteriophages as a biological antibacterial treatment to eliminate potential L. monocytogenes contamination on RTE sliced beef products (roast beef and pastrami).
Methods: For phage evaluation experiments, meat slices were cut and spot-inoculated with L. monocytogenes cultures (N = 5) and with (1000 MOI Phage) or without (PBS) phages, vacuum packaged, and incubated at 4°C for 30 days. Samples were collected at 0 h, 30 min, 2 h, 1 d, 2 d, 5 d, 7 d, 14 d, 21 d, and 30 days; diluted, plated on PALCAM plates, incubated at 37°C for 24 - 48 h, viable bacterial colonies were counted. Potassium lactate (4.8%) was also evaluated as an antimicrobial. Data analysis was done by plotting CFU/g as a function of time for all treatment points.
Results: Phage treatment results showed a sharp decline of Listeria counts (CFU/g) after 30 min in the vacuum packaged roast beef at 4°C. A ~4-log difference from the control was observed in 2 h and no viable cells were detected after 24 h. In contrast, L. monocytogenes cells without phage treatments had a steady survival rate with ± 0.5 log cycles variability; regression analysis data showed a slight death rate over 30 d at 4°C. Interestingly, with potassium lactate treatment (4.8%) in vacuum packaged roast beef stored at 4°C, no reduction of bacterial cells was observed.
Significance: Results showed bacteriophage treatment was highly effective to control L. monocytogenes in roast beef which can be used as an alternative to prevent any undesired contamination at 4°C.