On the antibacterial effects of manuka honey: mechanistic insights

 Antimicrobial resistance (AMR) is an increasing clinical problem precipitated by the inappropriate use of antibiotics in the later parts of the 20th Century. This problem, coupled with the lack of novel therapeutics in the development pipeline, means AMR is reaching crisis point, with an expected annual death rate of ten million people worldwide by 2050. To reduce, and to potentially remedy this problem, many researchers are looking into natural compounds with antimicrobial and/or antivirulence activity. Manuka honey is an ancient antimicrobial remedy with a good track record against a wide range of nosocomial pathogens that have increased AMR. Its inhibitory effects are the result of its constituent components, which add varying degrees of antimicrobial efficacy to the overall activity of manuka honey. The antimicrobial efficacy of manuka honey and some of its constituent components (such as methylglyoxal and leptosperin) are known to bestow some degree of antimicrobial efficacy to manuka honey. Despite growing in vitro evidence of its antimicrobial efficacy, the in vivo use of manuka honey (especially in a clinical environment) has been unexpectedly slow, partly due to the lack of mechanistic data. The mechanism by which manuka honey achieves its inhibitory efficacy has recently been identified against Staphylococcus aureus and Pseudomonas aeruginosa, with both of these contrasting organisms being inhibited through different mechanisms. Manuka honey inhibits S. aureus by interfering with the cell division process, whereas P. aeruginosa cells lyse in its presence due to the reduction of a key structural protein. In addition to these inhibitory effects, manuka honey is known to reduce virulence, motility, and biofilm formation. With this increasing in vitro dataset, we review the components and our mechanistic knowledge of manuka honey and how manuka honey could potentially be utilized in the future to impact positively on the treatment of microbial, resistant infections.