Identification of gallic acid in Trapa bispinosa as an effective inhibitor of the vegetative growth and spore germination of Paenibacillus larvae

Paenibacillus larvae is the etiological agent of American foulbrood (AFB) disease, a contagious bacterial disease that infects honeybees (Apis mellifera L.). Screening naturally occurring compounds to negate concerns related wide use antibiotics an urgent need for prevention and treatment AFB disease. In this study, we demonstrated crude ethanolic extracts (CEEs) from leaves Trapa bispinosa Roxb (TB) Euryale ferox Salisb (EF), as well fractions obtained by liquid–liquid extraction using petroleum ether, ethyl acetate (EA), n-butanol, possessed in vitro growth-inhibitory activities against local strain P. larvae, P.l.YZU. When combined with chloramphenicol, these plant exhibited additive mode interaction on P.l.YZU, suggesting potential application them control reduce conventional antibiotics. Our results showed CEEs TB higher antagonistic activity P.l.YZU than EF EA-fraction best MIC MBC values 250 500 μg/mL, respectively. Results LC–MS revealed gallic acid was most abundant compound present TB. Gallic could inhibit not only vegetative growth (with 125 respectively) through cell-membrane disturbing process, but also germination spores. The study highlighted effective antibacterial which provides alternative combat beekeeping practice.