Phenolic profiles and antimicrobial activity of various plant resins as potential botanical sources of Serbian propolis

Extensive employment of plant resins and propolis, as an antiseptic agents dating from ancient times in numerous cultures indicating that it may have antimicrobial and other biological properties. Resins from deciduous trees from the Populus and Salix genera, several fruit trees from the genus Prunus and a few other species were analyzed for their phenolic composition and antibacterial activity. Phenolic profiling of the plant resins was performed by high-performance thin-layer chromatography (HPTLC) and ultra-high-performance liquid chromatography (UHPLC) coupled with hybrid mass spectrometry. Antimicrobial activity against seven bacterial species was determined by minimum inhibitory concentration (MIC) assays and bioautography. The synergism, additivism, and antagonism of phenolic compounds were used to define the nature and type of interactions. Populus spp. showed higher amounts of p-hydroxybenzoic acid, p-coumaric acid, caffeic acid, chrysin, apigenin, quercetin, pinocembrin, pinobanksin and galangin, which confirmed the botanical origin of the orange and blue types of propolis. In addition, Gram-positive bacteria exhibited high susceptibility to poplar samples while being resistant to samples from other origins. Cherry bud samples had high amounts of naringenin and showed strong activity against Bacillus subtilis and Listeria monocytogenes. The combinations of tested phenolics showed mainly additive or indifferent effects.