Efficieny of Phage Intervention Against Salmonella in Meat and Poultry Processing

Abstract

ObjectivesPathogen Reduction, Hazard Analysis, and Critical Control Point systems final rule mandates establishments to seek and adopt antimicrobial interventions that can help in reducing the prevalence and most probable number of Salmonella in their meat and poultry products. Bacteriophages can aid in this challenge, as they can invade and kill specific target pathogenic bacteria on food products. Effective kill by phages relies on the appropriate phage application technique. Correct dose, good distribution on the food surface area, and adequate dwell time are key factors which influence phage-bacteria contact and thereby phage efficacy. This study determined the efficacy of a commercially available phage product, PhageGuard S consisting of 2 phages, FO1a, and S16. Different pick up levels, blend and hold times (chosen based on regulatory restriction and process limitations), as well as spray versus dip treatment methods were tested.Materials and MethodsOvernight culture streptomycin resistant Salmonella enterica enterica Enteritidis C (Se13) was diluted and inoculated at a concentration of 2×104 CFU/cm2 or CFU/g on parts of chicken fillet and held for 10 min for bacterial attachment (duplicate samples per time point). Subsequently, contaminated parts were spray treated with one phage concentration (108 Plaque Forming Units/g) at 0.5%, 1% or 3% pick up (v/w) or water (control) and blended for 5, 10, and 20 min before immediate grinding and retrieval of bacteria (latter blend time sample was held for 24 h before grind). Another set of contaminated fillet parts were treated by dipping in 5% phage solution (at 1% pick up, 108 PFU/g) and held for 1, 5, 10, and 20 min, and 1 and 24 h at 40°F (4°C) before retrieval of bacteria. Enumeration of bacteria was done on selective agar plates and reductions were calculated relative to water treated control.ResultsThe application of phages 108 PFU/g via spray on chicken parts at 3% pick up and 20 min blend time resulted in 0.9 log10 CFU/g log reduction of Salmonella. Additional hold time of 24 h before grind resulted in 1.1- 1.2 log10 CFU/g kill at lower and higher pick up of 0.5% and 3%. Dip treatment resulted higher Salmonella reduction of 1.2 log10 CFU/cm2 within 5 min of 108 PFU/cm2 phage application and up to 2.3 log10 CFU/cm2 log10 reduction when held for 24 h. Overall, the spray technique, showed a dose response effect where increasing pick up and blend time resulted in an increasing Salmonella kill in ground product. However, the dip technique resulted in more effective Salmonella kill in shorter dwell time. All values are mean value of two individual experiments.ConclusionThe above results indicate that the commercially available phage solution, PhageGuard S, either via spray or dip method reduces Salmonella contamination on meat and poultry parts by 1.2 to 2.3 log10, respectively. Thereby is an effective intervention in reducing risks and allowing for increase in consumer safety. Dip technique works better than spray due to better distribution on meat surface. Longer hold and/or blend time after phage treatment results in more kill.