The Antibacterial Activity of Honey

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Author
Henriques, Ana
Date
2006Type
Thesis
Publisher
University of Wales
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Honey is an old remedy recently rediscovered as a possible alternative to modern antibiotics in wound management but its mode of action is not fully understood. The antibacterial activity of honey can be divided into hydrogen peroxide and non-hydrogen peroxide-derived activity. This later type of activity is characteristic of honeys from Australasia (e.g. manuka honey) and preferred for wound management, although
historically local honeys have been used. The main aim of this study was to investigate
the mechanisms of antibacterial action of manuka honey. The stability of antibacterial
action of manuka honey under different conditions was determined, it was observed that
manuka honey lost its antibacterial activity when pH was increased and that it remained
the same with heating. Storage seemed to increase the potency of manuka honey. The
effects of honey on Staph. aureus and Pseud. aeruginosa, were investigated using
MIC/MBC detenninations, time-kill studies, commitment to death, resistance training,
electron microscopy, effects on respiration rates, leakage of intracellular material, and for
Staph. aureus the proteome of treated and non-treated cells were compared. It was
observed that the effect of manuka honey on Gram-positive and Gram-negative cells is
different. Gram-positive bacteria had a lower MIC than Gram-negative bacteria, but the
time-kill experiments and the commitment-to-deaths howed that Gram negative were
inhibited more rapidly. Clinical strains of both bacteria showed different time-kill profiles
to type strains. The methodology used for MIC determination was found to affect to the
results obtained. No honey-resistant ram-positive bacteria were recovered, but Gramnegative
bacteria were found to be able to become phenotypically resistant to manuka
honey. Electron microscopy showed that honey inflicted physical damages in both types
of cells, and in Gram-positive bacteria led to an increase in the proportion of population
of cells with a complete septum. Gram-positive cells incubated in honey increased their
endogenousre spiration rate whilst this was decreased in Gram-negative, major leakage
was observed in Gram-negative bacteria whilst only minor leakage was observed in
Gram-positive bacteria, which is consistent with the amount of damage observed with
electron microscopy. The proteome analysis of Staph aureus, revealed a general down
regulation of protein synthesis. Thirty Portuguese honeys were assayed for their
antibacteriaal ativity and honeys derived from Lavandulas toechas(lavender) were found
to possess non-peroxide activity. A selection of manuka honeys was screened for antimicrobial producing bacteria. In total 106 bacteria were recovered (85% were identified as Bacillus sp. ) and of those, 76 were capable of inhibiting the growth of at least one strain of bacteria tested, meaning that some of the antibacterial activity in
manuka honey could be due to the presence of antimicrobial agents of bacterial origin.
The antibacterial activity of manuka honey has previously been claimed to be due to
hydrogen peroxide production and not to a non-peroxide source of activity. A study of
free radical production and antioxidant potential demonstrated that manuka honey did not
produce any hydroxyl radicals via the Fenton reaction. Thus hydrogen peroxide could not
be present. It was also observed that even free radical-producing honeys were able to
quench radical production in vitro. In conclusion this study has demonstrated that the
non-peroxide activity of manuka honey is not exclusive to Australasia honeys, that it is
not derived from hydrogen peroxide generation and may have a microbial origin.
Furthermore the action of manuka honey on Gram-negative bacteria seems to be more
physical than in Gram positive where it appears to interfere with the cell physiology,
perhaps by stopping the cell cycle before cytokinesis.
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