Evaluation of In vitro Anti-Brucella Activity and Chemical Composition of Different Geographically-Distinct Propolis from Iran

Brucellosis is one of the most important zoonotic diseases in many regions worldwide. The aim of this study was to investigate antimicrobial properties of hydro-alcoholic extracts of 6 propolis (EEP) samples collected from different regions of Iran against 5 Brucella melitensis clinical isolates causing human brucellosis and an antibiotic-resistant Brucella abortus vaccinal strain (RB51). Brucella clinical isolates were first carefully identified using conventional molecular typing and Brucella biotyping methods. Different Brucella strains were then confronted to EEPs using the disk-diffusion agar method to evaluate the antimicrobial activity of each propolis extract.  Chemical composition of EEPs was then determined using HPLC-DAD and the main phenolic compounds were quantified. We found that all EEPs displayed significant antimicrobial activities against Brucella strains, although to varying extents.  All tested clinical strains were susceptible to different EEPs with inhibition zones ranging from 18 to 38 mm diameter. Interestingly, the RB51 vaccine strain was more susceptible to EEP6 (from Markazi province) when compared to conventional antibiotics used in the treatment of brucellosis. Substantial differences observed in EEP antimicrobial activity could be due to their distinct botanical origins and chemical compositions as confirmed by our HPLC analyses. The promising inhibitory effect of some propolis preparations against a broad spectrum of Brucella strains points to the need for further studies in the context of systematic clinical investigations and opens up the way for the development of natural complements in support of conventional antibiotic therapy.