Abstract
Background: Propolis consists of a complex mixture of resinous substances collected by honeybees from different plant sources. The objective of this study was to investigate the chemical composition, biological activities, and synergistic properties with antibiotics of propolis samples collected from various geographic origins (Germany, Ireland, and Czech Republic). Methods: The chemical composition of the propolis was analyzed by Gas Liquid Chromatography-Mass Spectrometry (GLC-MS) and High-performance liquid chromatography (HPLC). The minimal inhibitory concentration (MIC) and minimal bactericidal concentration (MBC) were evaluated by the standard broth microdilution method, while synergistic interactions were assessed by checkerboard dilution and time-kill curve assays. Results: HPLC and GLC-MS analyses revealed that ethanol extract of propolis (EEP) and water extracts of propolis (WEP) contained more than 100 different phytochemicals. The most abundant compounds were aromatic alcohols, aromatic acids, cinnamic acid and its esters, fatty acids, and flavanone (chrysin). Czech propolis showed the highest phenolic content (129.83 ± 5.9 mg CAE/g) followed by Irish propolis and German propolis. Furthermore, Irish propolis exhibited the highest value of total flavonoid content (2.86 ± 0.2 mg QE/g) and antioxidant activity (IC50 = 26.45 µg/mL). All propolis samples showed moderate antibacterial effect against Gram-positive microorganisms with MIC ranging from 0.08 mg/mL to 2.5 mg/mL. Moreover, EEP exhibited moderate activity against Gram-negative bacteria with MIC between 0.6 mg/mL to 5 mg/mL. In addition, EEP displayed moderate antifungal activity (MIC values between 0.6–2.5 mg/mL). The results obtained from time kill-kinetic assay and checkerboard dilution test of two-drug combinations between EEP and antibiotics such as vancomycin, oxacillin, and levofloxacin indicate mainly synergistic interactions against drug-resistant microbial pathogens including MRSA and VRE. Conclusions: The propolis extract synergistically enhanced the efficacy of antibiotics, especially those acting on cell wall synthesis (vancomycin and oxacillin) against drug-resistant microorganisms.
Highlights
Propolis is a sticky resinous substance produced by honey bees from different plant sources such as leaves, flowers, and bud exudates, modified by bee secretions and wax [1]
The propolis extract synergistically enhanced the efficacy of antibiotics, especially those acting on cell wall synthesis against drug-resistant microorganisms
Crude propolis collected from different geographical regions in Europe including Germany, Ireland, and Czech Republic were extracted with ethanol or water to study their chemical composition, antioxidant properties, and antimicrobial activity alone and in combination with antibiotics
Summary
Propolis (bee glue) is a sticky resinous substance produced by honey bees from different plant sources such as leaves, flowers, and bud exudates, modified by bee secretions and wax [1]. Propolis contain natural mixtures of different secondary metabolites that are responsible for various bioactivity such as antibacterial, anti-angiogenic, antiulcer, anti-inflammatory, antioxidant, and anti-viral activities [3]. Propolis contains various kinds of other secondary plant metabolites, which differ in concentrations depending on season, geographic origins of the collection and the proximity of a beehive to particular plant sources. Propolis consists of a complex mixture of resinous substances collected by honeybees from different plant sources. The objective of this study was to investigate the chemical composition, biological activities, and synergistic properties with antibiotics of propolis samples collected from various geographic origins (Germany, Ireland, and Czech Republic). All propolis samples showed moderate antibacterial effect against Gram-positive microorganisms with MIC ranging from 0.08 mg/mL to 2.5 mg/mL
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