Purpose: This study was developed to study the efficacy of bacteriophages for reducing Salmonella biofilms on surfaces and ultimately for preventing Salmonella re-contamination of rendered animal by-products and animal feed.
Methods: Salmonella isolates obtained from rendering facilities were characterized using pulsed field gel electrophoresis (PFGE) and serotyping analysis. Seven bacteriophages were selected for phage treatment based on evaluating host ranges of 94 bacteriophages against selected Salmonella isolates. Under laboratory conditions, the effectiveness of phage treatment with a multiplicity of infection (MOI) of 100 was evaluated against strong Salmonella biofilm formers using a colorimetric method in 96-well microplate. A greenhouse study was conducted to simulate real-world conditions in a rendering plant and phage treatment with MOI of 1,000 was applied for 7 days to reduce Salmonella biofilm formed on stainless steel surfaces in different seasons.
Results: A total of 34 samples (63%) were Salmonella-positive after enrichment and 166 Salmonella isolates were obtained sharing 31 different PFGE patterns and 16 different serotypes. The reduction of Salmonella biofilm reached up to 90% with phage treatment under laboratory conditions. In the greenhouse study, phage treatment reduced up to 3.4 log (99.96%) and 1.4 log (96%) CFU/cm2 of biofilm formed by Salmonella in summer (Ave. 28ºC; Ave. relative humidity: 67%) and fall/winter (Ave. 21ºC; Ave. relative humidity: 32%) seasons, respectively.
Significance: The results of this study demonstrated the effectiveness of phage treatment in reducing Salmonella biofilm on the surface of stainless steel under laboratory and greenhouse conditions. This suggests use of bacteriophages in rendering facilities that utilize stainless steel feed contact surfaces may have merit in reducing the likelihood of finished rendered products being re-contaminated with Salmonella.