Evaluation of the potential of phage phSE-5 to fight Salmonella Typhimurium in milk, liquid whole egg, and eggshell.

Aims: This study aimed to evaluate the potential of phage phSE-5 to inactivate Salmonella enterica serovar Typhimurium in milk (at 4, 10, and 25°C), liquid whole egg, and eggshell (at 25°C for both matrices).

Methods and results: Since the success of phage treatment in food depends on maintaining phage viability towards different food conditions, firstly the stability of phage phSE-5 at different temperatures and pHs was assessed. The effect of phage phSE-5 against S. Typhimurium was then assessed in vitro (liquid culture medium-TSB) and finally in the selected food matrices. Phage phSE-5 was stable for long storage periods (56 days) at pH 7-8 and 4-25°C. At 25°C, the efficacy of phage phSE-5 was matrix-dependent with differences in the sample, relatively to the bacterial control, of 2.7, 4.6, 1.8, and 1.3 log colony-forming units (CFU) ml-1 in TSB, milk, liquid whole egg, and eggshell, respectively. Also, phage phSE-5 led to reductions relatively to the initial bacterial concentration only in TSB and milk with 1.9 and 2.1 log CFU ml-1 reduction, respectively. Additionally, this phage was more efficient at 25°C in the tested matrices than at 10°C (no reduction and 1.7 log CFU ml-1 reduction in TSB and milk, respectively; maximum difference of 1.7 and 3.3 log CFU ml-1 in TSB and milk, respectively) and 4°C (no bacterial reduction/difference was observed in both TSB and milk). However, the decrease in temperature from 25 to 10°C slowed down bacterial regrowth after phage treatment.

Conclusions: Our results show that phages are promising and environmentally friendly candidates for use as biocontrol agents against S. Typhimurium in milk, liquid whole egg, and eggshell, allowing a reduction in energy costs if carried out at 10°C.