The antibacterial and antifungal effects of rhododendron derived mad honey and extracts of four rhododendron species

Abstract

The antibacterial and antifungal activities of mad honey and the crude extracts (leaves and flowers) of Rhododendron ponticum L. subsp. ponticum, Rhododendron luteum L., Rhododendron smirnovii L., and Rhododendron caucasicum L. (Ericaceae) were investigated. A total of17 microbial organisms belonging to 16 species of bacteria, namely Staphylococcus aureus, Streptococcus salivarius, Klebsiella pneumoniae, Escherichia coli, Salmonella enteritis, Streptococcus pneumoniae, Bacillus cereus, Listeria monocytogenes, Streptococcus mutans, Pseudomonas aeruginosa, Bacillus licheniformis, Micrococcus luteus, Bacillus subtilis, Proteus vulgaris, and Candida albicans were studied using a disk-diffusion and agar dilution (minimal inhibition concentration) method. The antimicrobial activity of the antibacterial and antifungal activity of the mad honey and the crude extracts obtained from the 4 Rhododendron spp. turned out to be more effective in the case of bacteria than against fungus. The antimicrobial activity against gram-positive bacteria was more pronounced than against gram-negative ones. Each of the crude extracts of the Rhododendron spp. and mad honey exhibited more or less pronounced antibacterial and antifungal potencies in the case of both gram-positive and gram-negative bacteria and fungus. In particular, the crude samples of Rhododendron caucasicum flowers (RCF), Rhododendron ponticumleaves (RPL) and Rhododendron ponticumflowers (RPF), and Rhododendron smirnoviileaves (RSL) showed antibacterial and antifungal activity against the tested organisms. The crude RCF sample required an MIC of > 0.5 mg/ml for S. enteritis, B. cereus, L. monocytogenes, and S. mutans and of > 2 mg/ml for C. albicans.