Propolis Extracts Enhance the Antimicrobial Activity of Slovenian: Chestnut, Forest and Flower Honeys

Because of the overuse and misuse of antibiotic, an increase in antibiotic resistance of pathogenic bacteria is evolving. Attention should be focused on natural alternatives to antibiotics, like propolis and honey. They all have strong antibacterial properties because of the active substances they contain. In the present study, the influence of P1 (water-soluble propolis (WSP) Greit 120) or P2 (phosphate buffer saline (PBS) propolis extract Lj. Center pH = 8.0) on antimicrobial activity of different Slovenian: chestnut honey (CH), forest honeys (FoH), and flower honey (FlH) against various Gram-positive or Gram-negative bacteria and yeast Candida albicans are shown. Gram-positive bacteria used in the experiments were: methicillin-resistant Staphylococcus aureus, Staphylococcus aureus, Streptococcus pyogenes, Streptococcus agalactiae and Streptococcus mutans. The yeast was Candia albicans. Gram-negative bacteria used were: Escherichia coli, Pseudomonas aeruginosa and Acinetobacter baumanii. P1, P2, FoH, CH, FlH and their combinations were prepared in saline as 10% solutions. The composition of both propolis extracts and the three kinds of honey was determined by reverse-phase high-performance liquid chromatography (RP-HPLC). It expressed the antimicrobial activity as a minimal inhibitory concentration (MIC) in mg/mL. Each of the two propolis extracts showed antimicrobial activity when applied alone. Also, the application of each of honey yielded an antimicrobial activity in decreasing order: CH, FoH and FlH honey. The combination of any of the propolis extract with any of the honey showed the additive antimicrobial effect on either Gram-positive or Gram-negative bacteria and on yeast Candida albicans. The effectiveness of P1 or P2 depends on their nature and from the sort of honey and is the highest in the case of CH followed by FoH and FlH.