Efficieny of Phage Intervention Against Salmonella in Meat and Poultry Processing

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.

Bacteriophage Intervention Effectively Kills Listeria on Food Contact Surface Materials

ObjectivesListeria is a pathogenic bacterium that is widespread in nature and can enter food processing plants through many vectors, like raw materials, process waste and personnel. Food processors work hard to keep Listeria out of the environment, but it can at times be found from food contact surfaces to floor drains. The sanitation can be compounded when equipment is pitted or cracked creating a harborage or niche in which Listeria can grow. Many control strategies for cleaning and biofilm removal have been put into place but may not suffice in eliminating Listeria from the food contact surface or environment. Bacteriophages are now being used to tackle these pathogens in food processing environments. Since they only target specific bacteria, they are harmless to humans, animals and plants, while effectively eliminating Listeria.This study determines the efficacy of a commercially available bacteriophage product, PhageGuard Listex, against Listeria on commonly found materials in food processing plants (stainless steel and UHMW polyethylene). Efficacy was determined by applying two phage concentrations, as well as two exposure times.Materials and MethodsOvernight cultures of L. monocytogenes ATCC13832 and L. innocua ATCC51742 were mixed in equal parts to create a Listeria cocktail (2 × 109 CFU/cm2). Sterile coupons (100 cm2) of stainless steel or UHMW polyethylene were artificially inoculated with the cocktail at 2.5ML/cm2 and left to dry at 37°C until completely dry. Subsequently, coupons were treated with 2 × 107 or 1 × 108 Plaque Forming Units (PFU)/cm2 using a spray system and incubated at room temperature for 1 and 3 h, before retrieval and enumeration of bacteria on selective agar plates. Sample size n:3. Results were analyzed using two-way ANOVA, with Dunnett’s multiple comparisons test on the normalized data.ResultsA dose dependent response to the phage treatment was observed, where an increasing phage concentration resulted in an increase in Listeria kill on both surfaces. On stainless steel, a treatment dose of 2 × 107 PFU/cm2 resulted in a statistically significant bacterial reduction of 1.27 log after 1 h (p value < 0.0001), while application of 1 × 108 PFU/cm2 showed a 2.16 log reduction (p value < 0.0001). On UHMW polyethylene, a bacterial reduction of 0.47 log was observed 1 h after applying 2 × 107 PFU/cm2, while the application of 1 × 108 PFU/cm2 led to a reduction of 1.95 log. However, these reductions were not statistically significant (p value > 0.05). After 3 h of treatment, the reductions were slightly higher in both materials (Table 3). After this time, the difference between control and 5% treatment on UHMW polyethylene obtained a p-value < 0.05.ConclusionPhage technology is an easy and safe intervention which can be used as an additional tool to control Listeria in processing environments. The above results indicate that the commercially available phage solution, PhageGuard Listex, can reduce Listeria contamination on food contact surfaces by 0.4 to 3.4 logs after 3 h of treatment.Table 3Log reduction of Listeria cells after applicatio nof two bacteriophage concentrations, measured at 1 and 3 h post phage treatment