In vitro study of the antimicrobial activity of European propolis against Paenibacillus larvae

Typical European propolis is an antibiotic substance derived from the resin of poplar, birch, and aspen buds. Here, we tested the ability of propolis originating from the resins of these plants to inhibit the in vitro growth of Paenibacillus larvae, the organism that causes American foulbrood, a fatal honeybee larval disease. The study involved GC-MS analysis of extracts from nine samples of propolis gathered from the temperate climate zone of Europe. The extracts showed noticeable differences in the content of flavonoids and other phenolic compounds. Despite the differences in chemical composition, all tested extracts inhibited the growth of P. larvae, with a minimum inhibitory concentration of 7.8 to 62.4 μg mL−1. It was found that not only did the content of flavonoids affect the strength of antimicrobial activity, but other phenolics, such as the phenylpropenoids hydroxycinnamyl sesquiterpenols, glycerides and benzoates also had an effect. This is the first report on the comparative activity of different types of European propolis against P. larvae.