Anti-biofilm properties exhibited by different types of monofloral honey

The increasing trend of antibiotic resistance by bacteria accentuates the necessity to exploit alternative potential therapeutic agents capable to act as effective and natural antibacterial agents. Therefore, use of honey as antibacterial agent back to ancient times. Aim of this study was to demonstrate the susceptibility of biofilm formation by different pathogens to some types of monofloral honey, Hedera helix (ivy), Arbutus unedo (strawberry tree), Lavandula angustifolia (lavender), sulla (Hedysarum coronarium), and Ailanthus altissima (tree of heaven). In addition, we assessed the capacity of the honey to block the metabolic changes taking place in the microbial cells included in the biofilm. The inhibitory action was variable. Listeria monocytogenes was the most sensitive bacteria, so that the formation of biofilm was inhibited up to 72.20 % (when we tested 11.42 microliters/ml of sulla honey) and never lower than 27.32% (by assaying 5.71 microliters/ml of lavender honey). Pseudomonas aeruginosa was less sensitive; however, some types of honey, such as tree of heaven and sulla, caused a biofilm inhibition up to 40.41% and 35.85%, respectively. The types of monofloral honey were able to act on the P. aeruginosa metabolism, with percentage of inhibition not inferior than 46.07% (with 11.42 microliters of ivy honey), reaching even 75.24% (with 11.42 microliters of tree of heaven honey). St. aureus, which showed greater resistance to the biofilm-inhibitory action of the types of honey, was instead more sensitive at the metabolic level, with percentages of inhibition reaching 61.63% (in the presence of the tree of heaven honey).