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Bacteriophage Based Interventions to Reduce the Dissemination of Salmonella in Pork Production, During Transportation and Holding


The carriage of Salmonella on pork continues to represent a key food safety issue. Through various lines of research it has become established that the pig environment, both on the farm and prior to slaughter (transporters and holding areas), can contribute significantly to the carriage of Salmonella. Such environments are difficult to sanitize and any benefits derived from increased sanitation are only short-lived due to rapid re-contamination by pigs. In the current project, the potential of bacteriophage (viruses that infect bacteria) to control Salmonella within pigs and their environment (farm, transporter and holding area) will be evaluated. The key benefits derived from bacteriophage include specificity to target host, self-perpetuating, self-limiting, stable, low-cost and non-toxic effects towards eukaryotes.
Baseline studies will isolate phage from samples derived from farms and processing environments. The proportion of lytic and lysogenic phage recovered from samples will be correlated to the genetic structure of Salmonella populations in terms of temporal stability and diversity. This will provide valuable knowledge on the role of bacteriophage in defining the persistence of Salmonella within the pig environment. More significantly, the results will enable an assessment to whether Salmonella exposed to bacteriophage develop resistance or if different (non-susceptible) genotypes become established. The latter can be addressed through using an appropriate combination of bacteriophage.
Candidate bacteriophage exhibiting strong lytic activity and broad host range will be taken forward for further study. Here the stability and replication of bacteriophage under different evironmental conditions (temperature, host cell density; phage:host cell ratio (MOI)) will be assessed. In addition, the ability of bacteriophage to replicate under simulated gastro-intestinal tract conditions will be determined. Bacteriophage exhibiting high environmental stability and ability to replicate under sub-optimal conditions will be evaluated as a Salmonella biocontrol method using animal and environmental models.

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Expected Impact of Project Outcomes on Food Safety in Ontario:
Evidence to date identifies the pig environment as the most significant source of Salmonella. Here, the pathogen not only can become desseminated within herds but also passed onto successive groups of pigs raised in the same environment.
The epidemiology of Salmonella within pigs and their environments is not well understood. On certain farms the pathogen can have a transient existence whilst on others the bacterium can become endemic. The role of bacteriophage in defining the persistence of Salmonella has not been considered to any great extent. The hypothesis of the current study is that farms exhibiting low prevalence of Salmonella harbor virulent bacteriophage that prevent endemic populations of the pathogen becoming established. If true then this will provide an effective, easy to apply (spray) method, for controlling Salmonella throughout the pork chain. Key to the success of bacteriophage based control strategies is selection of the appropriate cocktail of phages with a sufficient broad host range, environmental stability and method/frequency of application. Such factors will be studied in detail in the proposed work.
The output of the research will provide a greater understanding on the role of bacteriophage on the population dynamics of Salmonella associated with pigs. The study will also provide a relatively simple control strategy to ultimately reduce the carriage of Salmonella on pork carcasses.<P> For more information, please visit the <a href="; target="_blank">Ontario Ministry of Agriculture, Food & Rural Affairs (OMAFRA) Food Safety Research Program</a>.

Warriner, Keith
University of Guelph
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