Chemical characterization and in vitro antimicrobial activity of honeybee propolis and Scaptotrigona jujuyensis geopropolis against tomato pathogenic bacteria

Abstract

The antimicrobial activity of four concentrations of hydroalcoholic extracts from honeybee propolis and Scaptotrigona jujuyensis geopropolis was screened in vitro against five tomato pathogenic bacteria. The agar-well diffusion method was used and the tested bacteria were Clavibacter michiganensis subsp. michiganensis, Xanthomonas gardneri, Xanthomonas vesicatoria, Pseudomonas corrugata, and Pseudomonas mediterranea. The main chemical characteristics of propolis and geopropolis, including the polyphenol profile through HPLC-DAD, were also determined. Geopropolis raw sample presented higher values of moisture (7.78%), waxes (50.79%) and ashes (3.69%) than propolis (4.59%, 31.16% and 2.42% respectively). The total polyphenol content and the dry extract were higher in propolis hydroalcoholic extract (3.83 mg eq galic acid mL-1 and 7.87%, respectively) than in the extract of geopropolis (0.16 mg eq galic acid mL-1 and 0.15%, respectively). Chromatographic analysis confirmed the presence of caffeic acid, quercetin, 1,5,7-trihydroxy-flavanone, apigenin, pinobanksin, chrysin, pinocembrin, and galangin in both extracts. The antimicrobial assay showed significant differences between the hydroalcoholic extract activities, as well as between the sensitivity of the tested bacteria. Propolis hydroalcoholic extract dilutions had an inhibitory effect over four of the five tested bacteria, while geopropolis hydroalcoholic extract dilutions were only effective against C. michiganensis subsp. michiganensis, and to a lesser extent. The sequence of bacteria sensitivity to propolis treatments was: C. michiganensis subsp. michiganensis > X. gardneri > X. vesicatoria > P. corrugata. Pseudomonas mediterranea was not sensitive to any of the hydroalcoholic extracts. The antimicrobial activity of both extracts was dose-dependent where the most concentrated treatments were the most effective (15.0 mg mL?1 of geopropolis and 78.7 mg mL?1 of propolis dry extract, respectively). The polyphenol content and the HPLC-DAD profile of the hydroalcoholic extracts disclosed differences in chemical composition that helped to explain the outcomes of the in vitro assay. These results are a contribution to the characterization of bee bioactive products, specifically to propolis and geopropolis. This study indicates the likelihood of using propolis as a non-conventional strategy to control tomato bacterial diseases.