The Antibacterial Activity of Honey

 

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.