Propolis is a substance derived from antimicrobial plant resins that honey bees use in the construction of their nests. Propolis use in the hive is an important component of honey bee social immunity and confers a number of positive physiological benefits to bees. The benefits that bees derive from resins are mostly due to their antimicrobial properties, but it is unknown how the diversity of antimicrobial activities among resins might impact bee health. In our previous work, we found that resins from different North American Populus spp. differed in their ability to inhibit in vitro growth of the bee bacterial pathogen Paenibacillus larvae. The goal of our current work was to characterize the antimicrobial activity of propolis from 12 climatically diverse regions across the US against the bee pathogens P. larvae and Ascosphaera apis and compare the metabolite profiles among those samples using LC-MS-based metabolomic methods. Samples differed greatly in their ability to inhibit both bacterial and fungal growth in vitro, but propolis from Nevada, Texas, and California displayed high activity against both pathogens. Interestingly, propolis from Georgia, New York, Louisiana, and Minnesota were active against A. apis, but not very active against P. larvae. Metabolomic analysis of regional propolis samples revealed that each sample was compositionally distinct, and LC-FTMS profiles from each sample contained a unique number of shared and exclusive peaks. Propolis from Aspen, CO, Tuscon, AZ, and Raleigh, NC, contained relatively large numbers of exclusive peaks, which may indicate that these samples originated from relatively unique botanical sources. This is the first study to characterize how the diversity of bee preferred resinous plants in the US may affect bee health, and could guide future studies on the therapeutic potential of propolis for bees.
Bibliographical noteFunding Information:
Thanks to C. Foster (Hidden Valley Honey, Reno, NV), T. Seely (Cornell University, Ithaca, NY), R. Oliver (Scientific Beekeeping, Grass Valley, CA), P. Limbach (Western Colorado Honey, Silt, CO), W. Klett (Jamestown, ND), S. Cobey (University of California-Davis, Davis, CA), N. Euliss (USGS, Jamestown, ND), D. Tarpy (North Carolina State University, Raleigh, NC), J. Villa (USDA-ARS, Baton Rouge, LA), M. Ellis (University of Nebraska, Lincoln, NE), D. Sammataro (USDA, Tuscon, AZ), and the University of Georgia Bee Lab for contributing propolis samples; M.P. Cohen (Principal Statistician, American Institutes for Research, Washington, DC) for statistical help and advice; S. Cohen (Center for Regulatory Research, Roseville, MN) for help developing the fungal assay; F. Gleason and A. Hegeman (University of Minnesota) for reading and commenting on the manuscript; the Boswell/Cohen/Gardner/Hegeman and Spivak lab groups for useful discussions; and the NSF Plant Genome Research Program grants IOS-0923960 and IOS-1238812 , NSF grants IOS-0717530 , IOS-1256992 , and IOS-1256992 , the Charles J. Brand Endowment, the UMN College of Food, Agriculture, and Natural Resource Sciences, the National Honey Board, the Minnesota Agricultural Experiment Station, and the Gordon and Margret Bailey Endowment for funding.
- Apis mellifera
- Ascosphaera apis
- Honey bees
- Paenibacillus larvae