Antimicrobial Resistance to Honey
The major problem with most new antibiotics and antimicrobials is the rapid emergence of resistance. It was a matter of years between the discovery of penicillin and subsequent detection of penicillin-resistant microorganisms, and currently emerging bacterial resistance is occurring more rapidly than the development of new antibiotics.[45,46] To date, training experiments using manuka honey have not resulted in the emergence of resistant bacteria.[32,47] One of the reasons this might be is the combined effect of the many different honey components acting additively or synergistically, presenting too many different pressures for resistance to occur. Ordinarily, antibiotic or antimicrobial treatments target a particular process, such as cell wall synthesis, protein transcription or efflux mechanisms, and thus provide a specific evolutionary pressure to which microorganisms can adapt (Figure 2). The multiple targets affected by honey could therefore underpin its potency; affecting too many targets for bacteria to adapt to. Much work has been undertaken to identify the specific components of honeys and perhaps to develop drugs based on these individual constituents in the future; however, in light of the growing evidence describing the versatile action of manuka honey and the fact that this might be the key to preventing the emergence of resistance, this approach might not be best advised.
There have been concerted efforts to find novel antimicrobial therapies to combat the antibiotic crisis and there are studies showing that there are several natural products such as gallocatechins and curcuminoids that can enhance the action of currently used antibiotics.[48,49] It is feasible that as well as being an antimicrobial agent in its own right, honey could have the potential to be administered in combination with currently used antibiotics to improve their activity. Manuka honey acts synergistically with several antibiotics reducing the dose of antibiotics required to inhibit bacterial growth. Specifically, the synergistic action of manuka honey and oxacillin resensitizes MRSA to oxacillin treatment in vitro. Chequerboard assays were also used to demonstrate synergy between manuka honey and rifampicin, imipenem, mupriocin or tetracycline against S. aureus); in addition to synergy between manuka honey and rifampicin, tetracycline or colistin against P. aeruginosa. While these studies were only conducted in vitro (there are currently no in vivo data or clinical trials supporting these data) it is possible that they could eventually be translated into clinical practice to reduce doses for treatment and if resensitization is common, could allow the reintroduction of antibiotics to which there are currently high levels of resistance.
Future Microbiol. 2013;8(11):1419-1429. © 2013 Future Medicine Ltd.