Reduction of Salmonella in vitro and on the Surface of Chicken Breast Fillets by Bacteriophage Preparation

Introduction: Lytic bacteriophages are novel, natural antimicrobials that are increasingly recognized as GRAS (Generally Recognized as Safe) for their intended use in various food products. Recently, FDA has affirmed the GRAS designation of a Salmonella-targeted bacteriophage preparation. USDA has approved the same preparation as safe and suitable antimicrobial for use in the production of poultry products as an incidental processing aid.

Purpose: To determine the in vitro efficacy of Salmonella phage cocktail against different Salmonella serotypes and the effectiveness of phage preparation in reducing Salmonella on chicken breast fillets.

Methods: The effect of phage cocktail on the inhibition of growth of various Salmonella serotypes (Enteritidis, Hadar, Heidelberg, Kentucky, and Typhimurium) was determined using a 96-well plate assay by measuring the optical density at 630 nm. Diluted overnight cultures of Salmonella (10⁴ CFU/ml) were treated with bacteriophage at a multiplicity of infection (MOI) of 1, 100, 1000, 10000 PFU/CFU and incubated at 37°C for 48h. The efficacy of phage on reducing Salmonella at 4°C in TSB was determined by treating Salmonella cultures (10⁶ CFU/ml) with phage (MOI of 100, 1000, 10000) for 24h. Chicken breast fillets inoculated with a three-strain cocktail of Salmonella (Enteritidis, Heidelberg and Typhimurium ~10³ CFU/g) were treated with phage concentrations of 10⁷ PFU/g and stored up to 10d at 4°C.

Results: Bacteriophage preparation at 10000 MOI completely inhibited growth of Salmonella at 37°C for 48 hours. At 4°C, bacteriophage preparation caused ca. 4.5 log reduction of Salmonella up to 24h. On raw chicken breast fillets, phage application caused 1.2, 1.3, 1.8, and 1.7 log CFU/g reductions of Salmonella as compared to control on d 0, 1, 7, and 10 of storage at 4°C, respectively.  All reductions were statistically significant (P ≤ 0.05).

Significance: These findings indicate that the bacteriophage preparation is effective in reducing Salmonella on chicken breast fillets.  This phage cocktail could be an effective tool for reducing Salmonella on chicken parts during processing.