ANTIMICROBIAL ACTIVITY OF COMERCIAL PRÓPOLIS ALCOHOLIC EXTRACT

Currently the microbial resistance to allopathic antimicrobials represents a serious medical-social problem. Consequently, there is an increased interest on search for natural compounds with antimicrobial properties. Propolis has several pharmacological properties, highlighting its antimicrobial potential. The primary aim of this research was to examine the antimicrobial effects of propolis alcoholic extract on gram-negative and gram-positive bacteria, and to determine the minimum bactericidal concentration (MBC) for the species evaluated. Four bacterial strains was evaluated, two gram-negatives (Klebsiella pneumoniae ATCC 10031 and Salmonella typhimurium UK-1 and two gram-positives (Staphylococcus epidermidis ATCC 12228 and Enterococcus faecalis ATCC 29212). The colonies are stored at -20ºC in Luria-Bertani (LB) broth supplemented by glicerol 10%. Propolis alcoholic extract was commercially obtained. The antimicrobial activity was evaluated by use of broth microdilution method. For the analysis, eight propolis extract concentrations were evaluated, the highest one was 5.5% and the lowest one was 0.05%. Aliquots of 30 µL from bacterial cultures in the logarithmic growth phase were inoculated into tryptic soy broth (TSB), and cultivated for 18 hours at 37ºC. Cells were centrifuged and washed in PBS and the cell concentration was adjusted according to the 0.5 McFarland standard. The tests were performed on 96 wells polystyrene microplates, with a final volume of 200 µL (100 µL of propolis alcoholic extract and 100 µL of microbial inoculum). The microplates were incubated for 18 hours at 37°C and the MBC was determined by colony forming units (CFUs) in LB agar plates. For MBC it was considered the smallest concentration of the extract in which visible growth of the colonies in agar was not observed after incubation at 37ºC for 24 hours. The experiment was repeated three times. The antimicrobial activity of the propolis alcoholic extract was observed in all prokaryotes evaluated. The two gram-positive species showed more susceptibility to the propolis extract. Growth of E. faecalis and S. epidermidis was completely inhibited by the concentrations 1% and 1.5% of propolis extract. For the gram-negative species, the MBCs were 2.25% for S. typhimurium and 2.5% for K. pneumoniae. Following this study, the effect of propolis extract on biofilm formation by these species will be evaluated, as well as propolis performance on the in vivo pathogenicity of these microorganisms.