In vitro antimicrobial efficacy of honeydew honey and Calendula officinalis L. against Pseudomonas aeruginosa

The complex therapeutic potential of honey and medicinal plants is well documented by the literature, but discrepancies may be observed while comparing research results [1, 2]. Twelve honeydew honey samples from different Transylvanian geographical locations were investigated for their antibacterial properties based on the results of two diffusion assays that included Pseudomonas aeruginosa (n=10, strains isolated from bovine mastitis, and the reference strain Ps. aeruginosa ATCC 27853) as a relevant antibiotic resistant pathogen. Both screening tests indicated a strong inhibitory effect for eight samples when compared to the artificial honey and also that the development of growth inhibition zones was dose dependent. The most active samples were subjected alone and in combination with Calendula officinalis L. essential oil to minimum inhibitory concentrations assay using the broth microdilution method that pointed out values below those recorded for well or disc diffusion assays (MICs for honeydew honey ranged from 5% to 10% (v/v) and were even more reduced (up to 2 times) in association with Calendula officinalis essential oil). This study showed that Romanian honeydew honey manifested antibacterial activity against multi-drug resistant Pseudomonas aeruginosa isolates and also Calendula officinalis essential oil ability to enhance this potential.

Keywords: honeydew honey, Calendula officinalis, antibacterial

References: 1. Iauk L et al. (2003) Phytother Res 17: 599–604.

2. Majtan J et al. (2011) Phytother Res 25: 584–587.