CONICET | Buscador de Institutos y Recursos Humanos

The aim of this work was to compare the antimicrobial activity against Paenibacillus larvae and theantioxidant capacity of two Laurus nobilis L. extracts obtained by different extraction methods. Thehydroalcoholic extract was moreover added as supplementary diet to bees in field conditions to testbehavioural effects and colony strength. Both laurel extracts were subjected to different phytochemicalanalysis to identify their bioactive compounds. Antimicrobial activity was analyzed by the minimal inhibitoryconcentration (MIC) determination by means the agar dilution method. The hydroalcoholic extract(HE) was able to inhibit the bacterial growth of all P. larvae strains, with 580 mg/mL mean value. This betterantibacterial activity in relation to the essential oil (EO) could be explained by the presence of somephenolic compounds, such as flavonoids, evidenced by characteristic bands resulting from the FourierTransform Infrared Spectroscopy (FTIR) analysis. Antioxidant activities of the extracts were evaluatedby 2,2-diphenyl-1-picrylhydrazyl (DPPH) free radical-scavenging ability and ferric reducing antioxidantpower (FRAP) assays. The HE showed the highest antioxidant activity as measured by DPPH, with IC50values of 257 ± 12 lg/mL. The FRAP assay method showed that the HE was 3-fold more effective reducingagent than the EO. When the bee colonies were supplied with laurel HE in sugar paste an improvement intheir general condition was noticed, although neither the hygienic behavior nor the proportions of thebreeding cells varied statistically due to the treatment. In conclusion, the inhibition power against P. larvaeattributable to the phenolic compounds, the antioxidant capacity of the HE, and the non-lethal effectson adult honey bees on field trials suggest the HE of laurel as a promising substance for control Americanfoulbrood disease.

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