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