Throughout the year, our team of phage hunters has been focused on bacteriophages (phages) which specialise in infecting Mycobacterium smegmatis bacteria. Mycobacterium smegmatis replicates quickly and is non-pathogenic (Smith, 2003), making it an appropriate model organism to safely study other mycobacterial species. M. smegmatis shares a unique cell wall structure and partial genetic homology with Mycobacterium tuberculosis (Wikipedia, 2017), and our work with M. smegmatis is contributing to an international effort to develop new methods to combat Tuberculosis disease (TB).
But it’s not only humans that could benefit from a greater investment into phage therapy and bacteriophage research. The honey bee (Apis spp.) plays an integral role in insect pollination of flowering plants and food crops (Michigan State University, n.d.), however honey bee populations worldwide are threatened by the contagious bacterial disease American foulbrood (BeeAware, n.d.).
American foulbrood disease affects the larval and pupal stages of juvenile honey bees, and is caused by the bacterium Paenibacillus larvae (Alippi, Lo´pez, & Aguilar, 2002). P. larvae spores are ingested by honey bee larvae and begin to reproduce in the midgut, before progressing into tissues and causing death of the individual (Djukic et al., 2014). The disease can be identified in the field by a progressive discolouration of the larvae to brown and black (Alippi et al., 2002) before it dies and is reduced to a viscous material within its cell.
Characterisation of P. larvae bacteriophages could lead to an alternative treatment for the colonies of commercial beekeepers. Destruction of an entire hive by burning is often resorted to in order to prevent the spread of American foulbrood; other methods can be costly, and antibiotic treatment has been disallowed in many countries due to residual product being detected in the resulting honey (Beims et al., 2015). Research into these phages is relatively recent, with full genome sequences of six P. larvae bacteriophages being published in 2014 (Merrill, Grose, Breakwell, & Burnett), allowing for genomic analysis, comparison between the individuals sequenced, and identification of important genes. The University of Minho took a more specific approach to this research by exploring the potential of hydrolytic enzymes used in bacteriophage replication to control P. larvae (Oliveira et al., 2015).
Brigham Young University and the University of Nevada are investigating bacteriophage treatment of Paenibaccilus larvae in beehives. Yost, Tsourkas and Amy (2016) experimented with a cocktail of several different P. larvae phages, and were able to observe an increase in Apis mellifera larvae survival rates using post-infection and especially preventative treatments. Brigham Young University’s ‘Phage Hunters’ class has inspired undergraduates to research P. larvae phages and ways that they can be used to treat American foulbrood (Hollingshead, 2014). After isolating different phages, the host range of each was tested on 59 strains of Paenibaccilus larvae, and a cocktail was used to demonstrate complete protection, with 0% of treated hives developing American foulbrood, compared to an infection rate of 80% in untreated hives used in control experiments (Brady et al., 2017). Treatment using a phage cocktail was found by both studies to have no adverse impact on bee mortality rates.
Brigham Young University has also released an informative video summarizing their research in addressing American foulbrood, which gives an excellent educational overview without getting too technical (Brigham Young University, 2014):
This summer school I am undertaking a research project within Biosciences as part of my undergraduate degree. Pending permissions to work with Paenibaccilus larvae, I hope to initiate the first New Zealand-based contribution towards both a preventative and post-infection treatment for American foulbrood. In addition to being integral to the success and diversity of our national flora, apiculture (beekeeping) represents an important sector of our nation’s economy, and I am excited for the opportunity to support the growing health of this industry.
Alippi, A. M., Lo´pez, A. C., & Aguilar, O. M. (2002). Differentiation of Paenibacillus larvae subsp. larvae, the Cause of American Foulbrood of Honeybees, by Using PCR and Restriction Fragment Analysis of Genes Encoding 16S rRNA. Applied and Environmental Microbiology, 68(7), 3655-3660.
Bee Informed Partnership. (2013). American Foulbrood (AFB). Retrieved from https://beeinformed.org/2013/10/21/american-foulbrood-afb/
BeeAware. (n.d.). American foulbrood. Retrieved from http://beeaware.org.au/archive-pest/american-foulbrood/#ad-image-0
Beims, H., Wittmann, J., Bunk, B., Spröer, C., Rohde, C., Günther, G., . . . Steinert, M. (2015). Paenibacillus larvae-Directed Bacteriophage HB10c2 and Its Application in American Foulbrood-Affected Honey Bee Larvae. Applied and Environmental Microbiology, 81(16), 5411-5419.
Brady, T. S., Merrill, B. D., Hilton, J. A., Payne, A. M., Stephenson, M. B., & Hope, S. (2017). Bacteriophages as an alternative to conventional antibiotic use for the prevention or treatment of Paenibacillus larvae in honeybee hives. Journal of Invertebrate Pathology, 150, 94-100.
Brigham Young University. (2014). Bee Killers: Using Phages Against Deadly Honeybee Diseases. Retrieved from https://www.youtube.com/watch?v=rj9_QGBJN0w
Djukic, M., Brzuszkiewicz, E., Fünfhaus, A., Voss, J., Gollnow, K., Poppinga, L., . . . Daniel, R. (2014). How to Kill the Honey Bee Larva: Genomic Potential and Virulence Mechanisms of Paenibacillus larvae. PLoS ONE, 9(3).
Hollingshead, T. (2014). Using microscopic bugs to save the bees. BYU News.
Merrill, B. D., Grose, J. H., Breakwell, D. P., & Burnett, S. H. (2014). Characterization of Paenibacillus larvae bacteriophages and their genomic relationships to firmicute bacteriophages. BMC Genomics, 15(745).
Michigan State University. (n.d.). Pollination. Retrieved from http://www.canr.msu.edu/nativeplants/pollination/
Oliveira, A., Leite, M., Kluskens, L. D., Santos, S. B., Melo, L. D. R., & Azeredo, J. (2015). The First Paenibacillus larvae Bacteriophage Endolysin (PlyPl23) with High Potential to Control American Foulbrood. PLoS ONE, 10(7).
Smith, I. (2003). Mycobacterium tuberculosis Pathogenesis and Molecular Determinants of Virulence. Clinical Microbiology Reviews, 16(3), 463-496.
STD.GOV Blog. (2017). Bacterial Diseases. Retrieved from https://www.std-gov.org/blog/bacterial-diseases/#4-tuberculosis
Wikipedia. (2017). Mycobacterium smegmatis. Retrieved from https://en.wikipedia.org/wiki/Mycobacterium_smegmatis
Yost, D. G., Tsourkas, P., & Amy, P. S. (2016). Experimental bacteriophage treatment of honeybees (Apis mellifera) infected with Paenibacillus larvae, the causative agent of American Foulbrood Disease. Bacteriophage, 6(1).