Controlling Salmonella in Poultry using Bacteriophages

Public health concerns associated with high prevalence of foodborne salmonellosis, the emergence of antibiotic-resistant organisms and the identification of poultry meat and products as one of the most common sources of Salmonella support the need for new pathogen control strategies in the poultry industry. Scientific research has focused on the use of bacteriophages as therapeutic agents for humans and animals; however, limited studies have been conducted on bacteriophage application on food safety, especially on poultry. Therefore, the objective of this study was to evaluate the phage density and exposure time required to reduce Salmonella load on experimentally inoculated chicken meat.

In Experiment 1, serovars of Salmonella were tested for antimicrobial susceptibility and rifampicin-resistant isolates were generated. Cocktails of the serovars Enteritidis, Kentucky and Typhimurium (EKT), and Hadar and Heidelberg (HH), were inoculated on chicken breast samples to a target of 104 CFU/g. A mixture of three lytic bacteriophages, active against multiple Salmonella serovars was applied to chicken samples. A total of 84 samples (25 +/- 2 g) per each cocktail were distributed among a negative control, Salmonella-inoculated positive control, Salmonella-inoculated samples treated with the phage mixture at differing titers (105, 106, 107, 108, and 109 PFU/ml) with two identical samples at 0, 15, 30, 60, 120, 360 min at 4 degrees C. Experiment 2 evaluated nalidixic acid-resistant Salmonella Typhimurium among negative control, Salmonella-inoculated control (positive control), Salmonella with two phage titers (105 and 109 PFU/ml) at 0, 30, 60 and 120 min at 25 degrees C and 4 degrees C.

Results showed differences in means for Salmonella cocktail EKT ranged from 0.1 to 0.7 log10 CFU/g with 0.7 log10 for 108 PFU/ml, 30 min, 4 degrees C. For Salmonella cocktail HH, reductions ranged from 0.1 to 0.4 log10 CFU/g with 0.4 log10 on samples treated with 108 PFU/ml, 120 min, 4 degrees C. For the Experiment 2, a higher phage concentration (109 PFU/ml) at 120 min post-inoculation storage at 25 degrees C was required to yield a 0.9 log10 difference in means. These findings showed that higher concentrations of bacteriophage were more effective controlling Salmonella than lower ones at both temperatures. In addition, temperature, time and bacterial attachment may influence phage efficacy.