Iowa State’s Phage Seeks to Protect Swine on Farm
Bacteriophages – the friendly viruses that can wreak havoc on harmful bacteria – are being harnessed to beat back Salmonella in livestock. A phage invented and recently patented by food safety researchers at Iowa State University is the first phage to control the spread of Salmonella in swine and to prevent the bacterium from developing into a vehicle of foodborne illness.
“The pen isn’t the only place pigs get Salmonella,” said D.L. (Hank) Harris, an animal science researcher at ISU. “They’ve got Salmonella when they come in from the farm. It turns out that vaccine and probiotics have not been very successful in reducing Salmonella in lairage immediately before slaughter. So we’re using pigs in an acute infection model to evaluate bacteriophage.”
Harris’ work to find effective ways to use bacteriophage in pigs has been successful enough to warrant further study in a collaborative Food Safety Consortium project later this year. Harris will team with Billy Hargis, an FSC researcher who directs the University of Arkansas Poultry Health Research Laboratory, to explore ways to maximize production of bacteriophages and to determine its effectiveness against various types of Salmonella.
Hargis has been pursuing FSC-supported research on bacteriophages’ effectiveness against Salmonella in poultry. The work matches up well with Harris’ pursuit of livestock-oriented work that has been supported by the Biotechnology Research and Development Corp., a nonprofit organization funded by federal and private corporate money.
Market-weight pigs have been a particular problem because their rate of testing positive for Salmonella generally increases as they move from the farm to the holding pens to the slaughterhouse.
Salmonella infection comes from the environments to which the pigs are exposed – the transportation vehicles, the holding pens, the other pigs – and it comes quickly. “Healthy pigs become Salmonella culture positive in tissue samples within as few as three hours after infection resulting from exposure to Salmonella-infected pigs,” Harris said.
When released into infected animals, phages release their DNA into the host cells of pathogenic bacteria, where they then produce more phages that kill the host cells.
Harris’ team at ISU invented the Felix 0-1 phage to reduce Salmonella in livestock, which can be injected into the swine until about three hours before slaughter and still be effective in controlling Salmonella. The time window until the three-hour mark is significant because pigs are especially at risk of infection during those hours of being held in close quarters with other pigs.
“Intervention with Felix 0-1 phage treatment following exposure to Salmonella and prior to harvest is effective in reducing the amount of Salmonella in an animal,” Harris said. “Alternatively, treatment of animals prior to harvest will limit the risk of contamination of healthy swine by infected swine in the event the animals were exposed to Salmonella when housed with other animals or transported to the slaughterhouse.”
Using the Felix 0-1 phage between three and 24 hours before slaughter has an advantage over other phages because it is lytic – causing the destruction of certain cells – for the most common serotypes of Salmonella that are present in swine.
In addition to being administered to the animals orally, the Felix 0-1 phage can also be applied to the finished product to reduce Salmonella contamination. The phage can be applied to the surface of the beef, poultry, lamb or pork by spraying or soaking.
Bacteriophages have regained popularity in recent years as antibiotics have run up against increasingly resistant bacteria. Bacteriophages, which occur in nature, were discovered in the 1920s, Harris noted, and were used to treat diphtheria and other diseases.
“But as soon as penicillin came out in the 1940s, nobody wanted to work with phages anymore except the microbiologists,” he said. The microbiologists used them to study the insertion of genes in bacteria. Meanwhile, bacteriophage research and usage continued in the Soviet Union because the Communist bloc nations had difficulty obtaining antibiotics.
The new emphasis on bacteriophages has led to projects such as development of the Felix 0-1 phage. “Our research now is to see if we can make this a practical thing to do and if there is a company that would be interested in marketing phage as a product,” Harris said.