Abstract
New information has come to light about the biological activity of propolis and the quality of natural products which requires a rapid and reliable assessment method such as High Performance Thin-Layer Chromatography (HPTLC) fingerprinting. This study investigates chromatographic and chemometric approaches for determining the antimicrobial activity of propolis of Serbian origin against various bacterial species. A linear multivariate calibration technique, using Partial Least Squares, was used to extract the relevant information from the chromatographic fingerprints, i.e. to indicate peaks which represent phenolic compounds that are potentially responsible for the antimicrobial capacity of the samples. In addition, direct bioautography was performed to localize the antibacterial activity on chromatograms. The biological activity of the propolis samples against various bacterial species was determined by a minimum inhibitory concentration assay, confirming their affiliation with the European poplar type of propolis and revealing the existence of two types (blue and orange) according to botanical origin. The strongest antibacterial activity was exhibited by sample 26 against Staphylococcus aureus, with a MIC value of 0.5 mg/mL, and Listeria monocytogenes, with a MIC as low as 0.1 mg/mL, which was also the lowest effective concentration observed in our study. Generally, the orange type of propolis shows higher antimicrobial activity compared to the blue type. PLS modelling was performed on the HPTLC data set and the resulting models might qualitatively indicate compounds that play an important role in the activity exhibited by the propolis samples. The most relevant peaks influencing the antimicrobial activity of propolis against all bacterial strains were phenolic compounds at RF values of 0.37, 0.40, 0.45, 0.51, 0.60 and 0.70. The knowledge gained through this study could be important for attributing the antimicrobial activity of propolis to specific chemical compounds, as well as the verification of HPTLC fingerprinting as a reliable method for the identification of compounds that are potentially responsible for antimicrobial activity. This is the first report on the activity of Serbian propolis as determined by several combined methods, including the modelling of antimicrobial activity by HPTLC fingerprinting.
Highlights
Propolis is a natural sticky substance collected by honeybees (Apis mellifera L.) from the buds of numerous plant species, depending on the climate zone
High Performance Thin-Layer Chromatography (HPTLC) phenolic fingerprinting of Serbian propolis samples revealed the existence of two main botanically distinct types of propolis, an orange type characterized by intense orange and blue bands and pale green zones, and a blue type showing a chemical profile full of blue bands, confirmed by the application of different pattern recognition techniques [7]
The antimicrobial activity of the Serbian propolis samples against various bacterial strains was determined by a minimum inhibitory activity (MIC) assay
Summary
Propolis is a natural sticky substance collected by honeybees (Apis mellifera L.) from the buds of numerous plant species, depending on the climate zone. It is used by honeybees as glue, to fill cracks in hives, and as a protective barrier against intruders such as microbes, snakes, mice, etc. Propolis has been recognized as an official drug in London pharmacopeias since the 17th century, and it is still one of the most frequently used natural remedies in the Balkan States [2] It has only been in the last decades that scientists have investigated its constituents and its biological properties with regard to its ethnopharmacological use, e.g. its antiseptic and immunomodulatory properties. The antimicrobial effects of propolis are well documented against various bacteria, yeasts, viruses and parasites [2,4]
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