Honey in the Management of Infections

Nicholas Namias

In This Article

Evidence for the Antimicrobial Properties of Honey

The text of this section is summarized in Table 3 . In 1984 Obaseiki-Ebor and Afonya, from the University of Benin in Nigeria, reported on the anti-candidal effects of a distillate of honey in vitro[24,25]. They showed that 72 isolates of Candida albicans were all susceptible to the HY-1 fraction of honey distillate, whereas 10% of the isolates were variably resistant to nystatin, miconazole nitrate, or clotrimazole. Minimal inhibitory concentrations (MIC) were determined for this compound as well as for commercial antifungals as v/v%. The MIC 90 for HY-1 was 2 v/v%, as compared to mycostatin suspension with an MIC 90 of 0.5 v/v%. They did not elaborate on the chemical nature of the distillate or on the mechanism of action. They also did not comment on the osmotic activity of the solutions, but a 2 v/v% solution of a distillate of honey is not likely to have as great an osmotic effect as honey.

Willix et al. of the University of Waikato in New Zealand reported on the antibacterial activity of Manuka honey as opposed to other honeys[26]. They stated that the antibacterial effects of honey are due in large part to hydrogen peroxide derived from an enzymatic system intrinsic to unprocessed honeys. However, they cited a systematic review of commercially available honeys in New Zealand by Allen et al.[27], using an assay that controlled for the osmotic effects of honey and negated the effect of hydrogen peroxide by adding catalase to the assay. They found that the antibacterial effect of honey (tested against Staphylococcus aureus) varied widely among honeys, comparable to a range of between 2% and 58% w/v of phenol, in an almost Gaussian distribution. They proposed that an unidentified factor in a local honey, Manuka honey, was responsible for this effect. Descriptions of the chemical nature or proposed mechanism of action of this factor have not been published. Manuka honey is a variety of honey that comes only from New Zealand, from bees fed on the nectar of the Manuka bush, Leptospermum scoparium. Similar antibacterial activity has also been found in honey from bees fed on the nectar of Leptospermum polygalifolium, which is found in the wilds in Australia. Willix et al. tested Manuka and non-Manuka honey against a variety of wound-infecting species of bacteria. They found that the relative sensitivities of various organisms varied between the Manuka honey and other honeys, but that overall both types of honey can completely inhibit bacterial growth at concentrations below 11% v/v. Manuka honey, with catalase added to neutralize hydrogen peroxide, could still inhibit completely the growth of Staphylococcus aureus at a concentration of 1.8% v/v. The sugar content of the two honeys was the same, so they ascribed the different relative antibacterial effects of the honeys to a different, unknown activity in Manuka honey. Another comparison of Manuka and non-Manuka honey was undertaken in 1999[2], this time against Staphylococcus aureus isolates from clinical wound infections, at various dilutions and with the addition of catalase to inactivate hydrogen peroxide. The non-Manuka honey at a 25% v/v dilution, in the presence of catalase, had no detectable antibacterial activity, whereas the Manuka honey under these conditions had no loss of antibacterial activity in the presence of catalase. The authors noted also that the lowest concentration of sugar that has antibacterial activity against S. aureus is 29% v/v, and that the MIC values for Manuka honey (2-3% v/v) and non-Manuka honey (3-4% v/v) are well below the concentration at which osmolarity could be credited with the antibacterial activity.

Efem addressed the question of the osmotic effect of honey in 1992 by testing in vitro the antibacterial effect of honey and the effect of a sugar syrup with physical properties similar to honey[28]. He used a wide variety of bacterial and fungal isolates from clinical infections (Streptococcus pyogenes, Enterococcus faecalis, Staphylococcus aureus, Escherichia coli, Klebsiella pneumoniae, Proteus mirabilis, Pseudomonas spp., Pseudomonas aeruginosa, Bacteroides fragilis, Clostridium welchii, Clostridium tetani, Clostridium oedematiens) and incubated them on appropriate culture media with wells of the honey or sugar cut into the media. Zones of inhibition were measured. Honey was inhibitory against all bacteria tested except Pseudomonas aeruginosa and Clostridium oedematiens. The sugar syrup was ineffective against any of the bacteria tested, with the exception of moderate activity against Streptococcus pyogenes (the anaerobes were not tested against the sugar syrup). The fungi tested were all uniformly suppressed by honey at 100% concentration, but, when diluted to 50% and 20%, the honey lost efficacy against the fungi. The fungi were not tested with sugar solution.

In 1998, Wahdan et al. compared the antimicrobial activity of honey and a sugar syrup with the same sugar content as honey against 21 bacteria and 2 fungi[29]. They found that there was no difference in bacteriostatic activity between full-strength honey and sugar syrup, but that the honey was statistically significantly more bactericidal. At dilute concentrations, the honey was always more bactericidal and bacteriostatic. Because of these differences when concentration was controlled for, the authors invoked some other properties of honey as at least partially responsible for its antimicrobial activity. They also point out multiple references from the apiary literature describing "inhibines," which are suspected to be hydrogen peroxide and phenolic acids, among which caffeic and ferulic acids were identified in honey for the first time in their laboratory.

In conclusion, honey has been shown to be clinically useful in various settings involving soft tissue infections and non-healing wounds, and there appear to be some properties of honey that are controlling infection other than via the strictly osmotic effect. The caveat is that all of the data are generated from small studies, generally without rigorous statistical analysis. It is unlikely that the large studies with elaborate monitoring of protocol and professional statistical analysis will ever be done, as the expense of such studies is unlikely to ever be rewarded with the proceeds of honey sales to make such research financially feasible. The applicability of in vitro studies of antibacterial effects is unknown in vivo, but the clinical evidence suggests that honey may be useful in certain circumstances. Its use should be considered when more conventional therapies have failed. The usefulness in the management of Helicobacter pylori is less compelling, and in light of the other effective and safe treatments available, is probably not worth further investigation.