Inhibition and changes in antibiotic sensitivity of bacteria cultured aerobically and anaerobically in four medicinal honeys.

In recent years, antibiotic resistance has become a growing public health concern. Honey has recently been recognized as an effective antibacterial agent, especially in the inhibition of multiple drug-resistant bacteria and treatment of chronic and hypoxic dermatologic wounds. As a result, multiple medical-grade honeys are licensed by the NHS for topical application. Medihoney®, Medihoney® Wound Gel™, Surgihoney™ and Revamil® Gel are widely-used honey products, however literature providing direct comparisons between all four products does not exist. The following study therefore assessed the bacterial inhibition and changes in antibiotic sensitivity of common wound pathogens S. aureus and P. aeruginosa cultured aerobically and anaerobically in the four aforementioned products. Compositional analysis was also undertaken. To investigate the antibacterial properties of the honeys, aerobic and anaerobic broth culture assays were carried out. Aerobically, 25%, 50% and 75% and anaerobically, 50% and 75% honey solutions were compared to bacterial controls. To assess altered bacterial susceptibility to antibiotics, an agar disc diffusion assay using bacterial solutions preincubated in subinhibitory solutions of 10% honey was undertaken. Compositional analysis (measuring honey polyphenol content, antioxidant capacity, catalase, sugar, pH and colour) was also carried out. The results demonstrated that all honeys were bactericidal at 75%. Medihoney® was consistently bactericidal at all concentrations and Medihoney® Wound Gel™ was similarly effective, apart from aerobically at 25% against P. aeruginosa. Revamil® Gel provided the lowest levels of bacterial inhibition. For antibiotic sensitivity, Surgihoney™ significantly increased the sensitivity of both bacteria to the most antibiotics. Compositional analysis identified the polyphenol content and antioxidant capacity of Medihoney® and Surgihoney™ to be significantly higher than that of Revamil® Gel (p < 0.05). To conclude, significant differences between all honeys were observed. These have the potential to be positively exploited (for example, prioritising Medihoney® as an antibacterial agent while prioritising Surgihoney™ for use with antibiotics as dual-therapy to enhance antibacterial effects). Further research is warranted to understand the mechanisms of the observed differences to better match individual honeys to varying clinical diagnoses. Key words: honey, Manuka, wound healing, antibacterial, antibioti