In vitro activity of Bulgarian propolis against 94 clinical isolates of anaerobic bacteria

Abstract

The aim was to evaluate the effect of 30% ethanolic extract of Bulgarian propolis on 94 clinical anaerobic strains. The strains were tested by both agar-well diffusion (wells, 7 mm diameter) and disk-diffusion methods. Only 15% of Clostridium-, 3.3% of other Gram-positive- and 9.1% of Gram-negative anaerobic strains were not inhibited by 30 μL propolis extract per well. Propolis extract was more active than the ethanol ( P < 0.001 ). By 30 μL extract per well, mean inhibitory diameters of the clostridia, other Gram-positive- and Gram-negative anaerobes were 11.5, 13.1, and 11.3 mm, and those by 90 μL were 16, 18.1 and 15.4 mm, respectively. Mean inhibitory diameters of all strains by 30 and 90 μL ethanol were only 8.4 and 9.5 mm. By 30 μL propolis extract per well, inhibitory diameters of 15 mm or more were more common in Gram-positive (32%) than in Gram-negative bacteria (13.6%, P < 0.05 ). Moist propolis disks inhibited more strains (89.4%) than dried disks (68.1%, P < 0.001 ). Most (81.8%) Bacteroides fragilis group strains and 75% of clostridial strains were inhibited by moist EEP disks. Conclusion: Bulgarian propolis was active against most anaerobic strains of different genera. In addition to oral pathogens, an activity of propolis against Clostridium, Bacteroides and Propionibacterium species was observed. The results could motivate a higher medical interest and further trials for evaluating the use of bee glue for prophylaxis or treatment of some anaerobic infections such as oral, skin and wound diseases.