An investigation into the antibacterial mechanism of honey

Massoura, Maria (2020). An investigation into the antibacterial mechanism of honey. University of Birmingham. Ph.D.

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Abstract

The Antimicrobial Resistance, one of the biggest public threats of our times, emerged the development of alternative antibiotics. As such substances/procedures employed historically to cure diseases are now attracting the renewed interest of the scientific community. Honey has been empirically used as a powerful therapeutic since ancient times. However, currently the understanding of the underlying antibacterial mechanism is incomplete and this underestimates the medicinal value of honey.

This study aims to investigate the mechanism underlying the antibacterial activity of hydrogen peroxide (H\(^{2}\)O\(^{2}\))-producing honeys. To overcome the variability between honey species, a model system was used. This allowed to investigate the antibacterial effect of, and possible synergies between the three main stressors; sugars, gluconic acid and H\(^{2}\)O\(^{2}\), resulting from the enzymatic conversion of glucose, on honey dilution. The combination of cellular and genetic methods holds the key to understanding the bacterial stress responses towards honey. Multiparametric flow cytometry (FC) and atomic force microscopy (AFM) probed the physiological changes of E. coli K-12 while wide-genome transposon mutagenesis (TraDIS) identified genes and pathways which are involved in bacterial pathogenicity and resistance to honey.

The model honey revealed significant synergies occurring on honey dilution. The synergy of H\(^{2}\)O\(^{2}\) and gluconic acid augmented the antibacterial effect of honey by causing simultaneous cell membrane depolarization and destruction. TraDIS showed that switch to anaerobic metabolism consists the bacterial resistance mechanism to honey. Thus, the mutation of genes implicated in anaerobic metabolic activity, cellular homeostasis and membrane invagination caused a significant growth defect on the respective strains post-exposure to honey. These genes were deemed as “conditionally essential” as encode functions that are absolutely vital for cell viability on honey.

As a proof of concept, the antibacterial effects of natural honeys was tested in vitro in a coculture of two pathogenic species, E. coli (UPEC)-C. albicans, implicated in vulvovaginal infections. Both pathogens were fully susceptible to honey of high acidity and high H\(^{2}\)O\(^{2}\) accumulation which confirmed the importance of this synergy in antibacterial strength of honey.

Overall this thesis presents a comprehensive and novel approach towards the understanding of the antibacterial mechanism of honey. This is expected to provide an advanced explanation on the mechanistic action and reveal further potential medicinal applications of this natural product.

Type of Work:

Thesis (Doctorates > Ph.D.)

Award Type:

Doctorates > Ph.D.

Supervisor(s):