How honey kills bacteria

Manuka Honey has been renowned for its wound-healing properties since ancient times. At least part of its positive influence is attributed to antibacterial properties. With the advent of antibiotics, clinical application of honey was abandoned in modern Western medicine, although in many cultures, it is still used. These days, however, abundant use of antibiotics has resulted in widespread resistance. With the development of novel antibiotics lagging behind, alternative antimicrobial strategies are urgently needed. The potent in vitro activity of honey against antibiotic-resistant bacteria and its successful application in treatment of chronic wound infections not responding to antibiotic therapy have attracted considerable attention.

The broad spectrum antibacterial activity of honey is multifactorial in nature. Hydrogen peroxide and high osmolarity – honey consists of 80% (w/v) of sugars – are the only well-characterized antibacterial factors in honey. Recently, high concentrations of the antibacterial compound methylglyoxal (MGO) were found specifically in Manuka honey, derived from the Manuka tree (Leptospermum scoparium). Until now, no honey has ever been fully characterized, which hampered clinical applications of honey.

How honey kills bacteria. FASEB Journal, 2010. doi: 10.1096/fj.09-150789
With the rise in prevalence of antibiotic-resistant bacteria, honey is increasingly valued for its antibacterial activity. To characterize all bactericidal factors in a medical-grade honey, we used a novel approach of successive neutralization of individual honey bactericidal factors. All bacteria tested, including Bacillus subtilis, methicillin-resistant Staphylococcus aureus, extended-spectrum β-lactamase producing Escherichia coli, ciprofloxacin-resistant Pseudomonas aeruginosa, and vancomycin-resistant Enterococcus faecium, were killed by 10–20% (v/v) honey, whereas 40% (v/v) of a honey-equivalent sugar solution was required for similar activity. Honey accumulated up to 5.62 ± 0.54 mM H2O2 and contained 0.25 ± 0.01 mM methylglyoxal (MGO). After enzymatic neutralization of these two compounds, honey retained substantial activity. Using B. subtilis for activity-guided isolation of the additional antimicrobial factors, we discovered bee defensin-1 in honey. After combined neutralization of H2O2, MGO, and bee defensin-1, 20% honey had only minimal activity left, and subsequent adjustment of the pH of this honey from 3.3 to 7.0 reduced the activity to that of sugar alone. Activity against all other bacteria tested depended on sugar, H2O2, MGO, and bee defensin-1. Thus, we fully characterized the antibacterial activity of medical-grade honey.

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