Remember the plague that befell kiwifruit after the pathogen PSA was first detected in New Zealand in 2010? Plant scientists have since managed to breed a variety that is resistant to the canker-causing bacterial infection, but this is not the only microbial disease with potential to devastate a food industry.
Take American foulbrood, which affects honeybees and forces beekeepers to destroy any infected hives because they are not allowed to use antibiotics. This pathogen has been in New Zealand for almost 150 years after first being discovered in 1877. An eradication plan has been in place for more than a decade, but the disease lingers and continues to affect hives.
Better protection for both kiwifruit and honeybees may soon come in the form of microscopic biological control agents, bacteriophages. Bacteriophages – or just phages for short – are viruses that attack specific bacteria, explains Heather Hendrickson, a microbiologist at the University of Canterbury and co-leader of a project that received an $8.94 million funding boost to test a phage-based prophylactic treatment against bacterial diseases in various primary industries.
In the case of American foulbrood, the pathogenic microbe is Paenibacillus larvae. “Any beekeeper will tell you that this is a terrible thing,” Hendrickson says. “You have to check your hives on a regular basis and if you find that one has been infected, you need to burn it within seven days by law. There’s nothing you can do to prevent it right now.”
The bacteria can persist in the soil as dormant spores for at least 30 years. But that same soil probably also contains phages specific to this pathogen. Hendrickson and her team have enlisted beekeepers to collect samples of dirt around their hives and so far found 26 different phages that attack the American foulbrood pathogen.
Named Barry Foster after a Gisborne beekeeper or Bloomfield after the former director-general of health – or just simply Bob, Lena and Ted – these phages have already been tested in bench-top experiments against an array of bacterial strains that cause American foulbrood. But the next step is the animal disease equivalent of a clinical trial. “We can see which of the phages are able to infect 90% of the pathogens, or 40%, or only certain ones and not others. We can now combine the phages into a cocktail and the idea is that we’ll be able to put those in beehives.”
First, the phage cocktails will be tested on bee larvae, infected or healthy, to make sure the treatment is safe and effective. Ultimately, Hendrickson wants to see how well phages protect entire hives, without affecting honey production. “This will be similar to the treatments we put in beehives now to prevent the bee mite Varroa. This would hopefully inoculate the hives with this collection of phages that have a protective effect against American foulbrood.”
Hendrickson’s plan is to be able to offer effective preventive phage therapy for several primary industries to help reduce the use of antibiotics in animals to avoid further build-up of resistance. Of course, bacterial pathogens can also become resistant to phages, but by refining the phages she already has, and continuing the search for new ones, she hopes to stay a step ahead in this arms race.
Incidentally, she says, all phages have come from healthy hives. “One of the nice things is that healthy hives already have some of these protective phages. Our job is going to be to make sure that all hives have phages to keep them healthy.”
Hendrickson’s colleague in this project is University of Otago microbiologist Peter Fineran, who’s already collected phages that help kiwifruit fight off PSA and is preparing to test some cocktails in field trials. Between them, they plan to keep improving phage therapies against PSA and American foulbrood and start searching for new phages to help fight disease-causing microbes that infect salmon and cherries.
