Antibacterial effect of Manuka honey on Clostridium difficile

BACKGROUND: Manuka honey originates from the manuka tree (Leptospermum scoparium) and its antimicrobial effect has been attributed to a property referred to as Unique Manuka Factor that is absent in other types of honey. Antibacterial activity of Manuka honey has been documented for several bacterial pathogens, however there is no information on Clostridium difficile, an important nosocomial pathogen. In this study we investigated susceptibility of C. difficile to Manuka honey and whether the activity is bactericidal or bacteriostatic. METHODS: Three C. difficile strains were subjected to the broth dilution method to determine minimum inhibitory concentrations (MIC) and minimum bactericidal concentrations (MBC) for Manuka honey. The agar well diffusion method was also used to investigate sensitivity of the C. difficile strains to Manuka honey. RESULTS: The MIC values of the three C. difficile strains were the same (6.25% v/v). Similarly, MBC values of the three C. difficile strains were the same (6.25% v/v). The activity of Manuka honey against all three C. difficile strains was bactericidal. A dose-response relationship was observed between the concentrations of Manuka honey and zones of inhibition formed by the C. difficile strains, in which increasing concentrations of Manuka honey resulted in increasing size of zone of inhibition formed. Maximum zone of inhibition was observed at 50% (v/v) Manuka honey and the growth inhibition persisted over 7 days. CONCLUSION: C. difficile is appreciably susceptible to Manuka honey and this may offer an effective way of treating infections caused by the organism.