Purpose: This study was conducted to test the efficacy of bacteriophage cocktail for reducing Salmonella contamination of workers’ boots and ultimately for preventing Salmonella re-contamination of rendered animal meals.
Methods: Under laboratory condition, biofilms of Salmonella strain 8243 formed on the boots were treated with phage cocktail (9 log PFU/ml) alone, phage + bleach (400 ppm chlorine), and phage + scrubbing for 6 h in a boot bath. SM buffer and bleach alone were used as controls. A field study was conducted by treating workers’ boots with the same phage treatments for 1 week in rendering processing environment, in which all treatments were applied at a rate of 3 times per week. Indigenous Salmonella populations were swabbed and enumerated on XLT-4, Miller-Mallinson or CHROMagar plates.
Results: Under laboratory condition, Salmonella biofilms formed on the boots were reduced by 1.07 log (91.5%), 1.18 log (93.4%), 2.08 log (99.2%) and 1.52 log (97.0%) CFU/boot after treated with phage cocktail alone, bleach alone, phage + scrubbing and phage + bleach for 6 h, respectively. In a rendering processing environment (Ave. 19.3ºC; Ave. relative humidity: 48%), indigenous Salmonella populations on workers’ boots were reduced by 0.81 log (84.5%), 1.17 log (93.2%), and 1.15 log (92.9%) CFU/boot after treated with phage cocktail alone, phage + scrubbing, and phages + bleach for 1 week, respectively. Our results demonstrated the effectiveness of phage treatments in reducing Salmonella contamination on the boots in both laboratory and rendering processing environment.
Significance: Control of Salmonella contamination on workers’ boots can reduce the chances for the finished animal meals being re-contaminated with Salmonella, and therefore ensure the microbiological safety of rendered animal meals.