Bacteriophages as an alternative to conventional antibiotic use for the prevention or treatment of Paenibacillus larvae in honeybee hives

•39 phages tested for lysis in 59 P. larvae field isolates.•Phage treatment does not affect standard bee death rates.•Antibiotics reduce overall bee health, whereas phage treatment does not.•Phages protect against American Foulbrood in hives exposed to P. larvae.•Phages cure hives sick with American Foulbrood.

American Foulbrood (AFB) is an infectious disease caused by the bacteria, Paenibacillus larvae. P. larvae phages were isolated and tested to determine each phages' host range amongst 59 field isolate strains of P. larvae. Three phages were selected to create a phage cocktail for the treatment of AFB infections according to the combined phages' ability to lyse all tested strains of bacteria. Studies were performed to demonstrate the safety and efficacy of the phage cocktail treatment as a replacement for traditional antibiotics for the prevention of AFB and the treatment of active infections. Safety verification studies confirmed that the phage cocktail did not adversely affect the rate of bee death even when administered as an overdose. In a comparative study of healthy hives, traditional prophylactic antibiotic treatment experienced a 38 ± 0.7% decrease in overall hive health, which was statistically lower than hive health observed in control hives. Hives treated with phage cocktail decreased 19 ± 0.8%, which was not statistically different than control hives, which decreased by 10 ± 1.0%. In a study of beehives at-risk for a natural infection, 100 ± 0.5% of phage-treated hives were protected from AFB infection, while 80 ± 0.5% of untreated controls became infected. AFB infected hives began with an average Hitchcock score of 2.25 out of 4 and 100 ± 0.5% of the hives recovered completely within two weeks of treatment with phage cocktail. While the n numbers for the latter two studies are small, the results for both the phage protection rate and the phage cure rate were statistically significant (α = 0.05). These studies demonstrate the powerful potential of using a phage cocktail against AFB and establish phage therapy as a feasible treatment.

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