Phages are very specific in killing a limited range of bacterial strains, cf. antibiotics, and do not cause infections of animals or plants. Replication of a lytic phage results in lysis and killing of the host bacterium, increasing phage numbers considerably, in comparison with antibiotic therapy. Research has identified phages which kill Salmonella, Campylobacter, and other pathogenic bacteria, and established rapid, simple methods for amplification of phages to very large numbers. Recent work has shown phages to be effective in removing contamination from poultry carcasses, and also in killing pathogens in the intestinal tract of live poultry and in eggs. Using this phenomenon to protect or "cure" infected animals is the focus of ongoing investigations.
This project is focused on trials in live poultry to evaluate the importance of the following factors on safety and quality (WP6): phage choice and production (WPs 2, 4); route of administration and timing of administration (WP5); quantity of phages administered (WP5); modeling of the infection and curing process (WP3).
Alternative strategies were also considered for potential constraints related with development of phage-resistant strains of pathogens; mass application causing environmental concerns; and destruction of phages by stomach acidity following oral administration.
Antibiotics are currently being phased out of food animal production but alternative methods are needed to combat bacterial diseases in food animals and to control transmission of pathogens responsible for food-borne illnesses to humans.
Potential alternatives are few: Competitive Exclusion (CE) and Bacteriophage (phage) Therapy represent two of the most promising alternatives. Whilst there is one approved CE product on the market, commercial use is limited due to very high costs of production, highly restricted means of administration, and reduced efficacy.
The Phagevet-P project aims to evaluate the potential use of phages as alternatives to antibiotics in poultry production and to characterize the efficacy of phages from farm-to-fork. The particular bacteria common in poultry and pathogens for humans, to be addressed are Salmonella spp., and Campylobacter spp.. It is not intended in this project that large-scale rearing and treatment of birds will be carried out. This scale of experiment must await the "Proof of Principle" that this project will provide, although if this proof is achieved, treatment on the scale of several 100s of birds may be warranted.
The first scientific objective is to establish that in live poultry, treatment with specific phages can reduce or eliminate the occurrence of the two pathogens responsible for the majority of human food-borne illness, namely Salmonella and Campylobacter spp.
The second major objective is to establish that this protection of the live birds from infection, provides poultry products for human consumption that have greatly reduced contamination levels with these two pathogens.
In order to achieve these scientific objectives, several smaller technological objectives must be achieved, namely:
Many strains of Salmonella and Campylobacter have been isolated from poultry in Portugal and the UK. Phages active on these pathogens have been obtained from culture collections, but the majority being used in the project have been isolated from poultry sources in the UK, Portugal and Russia. The lytic spectra of the phages were determined on a group of more than 200 clinical and food isolates of different serotypes of both pathogens. A small number of lytic phages were selected for the bird trials and large-scale production and purification methods were evaluated. Initial modelling of bacterial growth and phage infection in culture has been developed. The genomes of some of the Salmonella phages have been examined and shown not to carry any Salmonella genes, indicating a very low likelihood of carriage and potential transfer of pathogenic traits. It is expected that the genomes of the Campylobacter phages will also be shown not to carry pathogenicity islands. In vivo trials have shown that the phages selected and characterised offer a good potential to control Salmonella and Campylobacter in vivo, but its efficacy is time dependent. Methods of application of the phages onto poultry were developed and assessed for potential large-scale use.
Reduction or elimination of the widespread use of antibiotics in poultry feed and replacement by prophylactic application of phages, in large-scale poultry rearing.
Transmission electron micrograph (TEM) of a Salmonella bacteriophage isolated from poultry sewage
Experimental groups of salmonella infected layers