Reduction of Artificial Salmonella Typhimurium Contamination on Stainless Steel by Application of Bacteriophage

Introduction: Bacteriophages have been studied as natural bactericidal agents for decontamination of fruits, vegetables, and animal hides.  The effectiveness of bacteriophage to reduce bacterial contamination on food contact surfaces such as stainless steel remains to be extensively studied. 

Purpose: The objective of this study is to test the effectiveness of a phage cocktail for reducing S. Typhimurium on artificially contaminated stainless steel surface at 4° and 22°C. 

Methods: Bacteriophages that cause lysis of Salmonella were isolated from raw sewage samples collected from four local water treatment plants.  Five isolates with different host ranges were selected and combined into a phage cocktail.  Sterile stainless steel spatulas were artificially contaminated by soaking a 14-cm² area in S. Typhimurium cell suspension prepared in phosphate buffer saline (PBS) for 1 h, and dried for 2 h at 22°C.  The contaminated areas were then soaked in PBS or the phage cocktail at 4 or 22°C for 2 or 24 h. 

Results: The mean initial Salmonella count was 7.3 log CFU/sample  Soaking contaminated stainless steel surface in a phage cocktail for 2 h resulted in about 2 log reduction in Salmonella counts at both 4 and 22°C.  Soaking additional 22 h in the phage cocktail did not cause significant more reduction in Salmonella counts.

Significance: Bacteriophages have been proven to reduce bacterial contamination on many food surfaces. This study shows that treating a stainless steel surface with a bacteriophage cocktail for 2 h could reduce Salmonella contamination by 2 logs at both 4 and 22°C.