Study of the antimicrobial and antibiofilm activity of romanian propolis

Although antibiotics have drastically reduced illness and death from infectious diseases, bacteria have exibited a remarkable capacity to quickly become resistant to antibiotics. The increase in antibiotic resistance is thus a global problem, due to the increased incidence of opportunistic infections with bacterial strains, aggravated by producing bacterial biofilms on cell substrates or biomaterials used in medicine. The emergence of multidrug-resistant phenomena caused an increasing concern and sustained researches for finding new antimicrobial agents or new therapeutical strategies for infectious diseases. In recent years, following the general trend of using direct resources provided by nature, bee products too have became an important source for different active factors, essential to promote a range of harmless therapeutic drugs. Among these, propolis is one of the strongest challenges to nutritionists and medical world due to the recognition of its high biological value and both prophylactic and therapeutic effects. The chemical composition of propolis is very complex and varies according to the geographical area and plant origin. The purpose of this study is to demonstrate the antimicrobial and antibiofilm activity of propolis from Romania on some Gram positive and Gram negative clinical bacterial strains. The tested product was 30% propolis tincture (propolis ethanolic extract = PEE) from Romania. PEE antibacterial activity was qualitatively and quantitatively evaluated by two methods: modified agar difussion method and serial two-fold microdilution method. The antibiofilm activity of propolis was determinated by the assay of its inhibitory influence on microbial biofilm formation on inert substratum. The microbial strains used were: Staphylococcus aureus, Escherichia coli, Klebsiella pneumoniae, Pseudomonas aeruginosa. The qualitative screening releaved that the PEE exerted an antimicrobial action against all tested bacterial strains, evidenced by the appearance of growth inhibition zones. The quantitative analysis of antimicrobial activity of PEE showed that the product exerted an inhibitory effect up to a concentration of 0.1875mg/ml against S. aureus. Also, the results revealed that S. aureus biofilm development on inert substratum was inhibited by propolis tincture at a concentration of 0.1875 mg/ml. The inhibitory activity of PEE against biofilm formation of Gram positive bacteria (S. aureus) and the positive results of qualitative screening tests on all tested Gram positive and Gram negative bacterial reference strains belonging to clinic