The characterisation of the antimicrobial activity of honey on clinical isolates of multi-drug resistant bacteria implicated in healthcare associated infections

Kenny, Jacqueline M. (2013) The characterisation of the antimicrobial activity of honey on clinical isolates of multi-drug resistant bacteria implicated in healthcare associated infections. (PhD thesis), Kingston University,


Bacterial resistance to antibiotics has presented increasing challenges in healthcare and the management of infection. This has resulted in alternative and traditional products that are used in other cultures being considered as an alternative to topical antibiotics. Honey, particularly Manuka honey is a product which has gained credibility as an antibacterial agent in a healthcare environment. The aim of this study was to investigate the antimicrobial capacity of syrups and honeys from different floral sources on antibiotic sensitive and resistant bacteria isolated from a clinical environment. The antimicrobial activity of seven Manuka honeys, seven honeys from other floral sources and two syrups were assayed against antibiotic sensitive and resistant isolates of 'Staphylococcus aureus', 'Enterococcus species', 'Escherichia coli' and 'Pseudomonas aeruginosa' using agar diffusion and microbroth methods to determine minimum inhibitory concentrations. These assays demonstrated both the superior antimicrobial activity of the Manuka products and highlighted differences in susceptibility between sensitive and resistant strains within organism groups. Clinical grade Manuka honeys were used to study the effect of bioload on antimicrobial efficacy on isolates from clinical polymicrobial wound populations. This demonstrated that it was the direct physical contact with the organism and not the microbial bioload which influences antimicrobial efficacy. Bacteria may form biofilms when they come into contact with an adherent surface. Organisms in biofilms have greater resistance to antimicrobials and are recognised clinically as a feature of chronically infected wounds. The ability of medical grade Manuka honey to remove established biofilms from a variety of surfaces was investigated. The results indicated potential activity but were inconsistent due to the fragility of biofilm adherence to artificial surfaces. To better emulate a clinical environment a wound model was designed using cooked meat and the polymicrobial bacterial populations from clinical wounds. The results of these experiments showed the Manuka honeys to have a bacteriostatic effect on the biofilms with no contamination of the surrounding honey medium. Chemical analysis of the honey products was performed using thin layer chromatography (TLC) and diffusion ordered spectroscopy nuclear magnetic resonance (DOSY NMR). TLC demonstrated the presence of antimicrobial fractions but insufficient material was yielded for further analysis and identification using NMR. Using DOSY NMR directly on the untreated honey products enabled characterisation of the products, identifying aromatic compounds in the Manuka products which are reputed to have antimicrobial activity. There did not appear to be any single constituent proportional to the antimicrobial UMF rating (Unique Manuka Factor) of the Manuka products where a high rating indicates a high level of antibacterial activity. The results suggest that it is a combination of compounds which confer the antimicrobial properties of the Manuka products. In conclusion this study demonstrated the superior antimicrobial activity of Manuka honey compared to syrups and honey from other floral sources and that this activity is likely due to a number of aromatic compounds present only in the Manuka products. Clinical grade Manuka honey appears to have bactericidal activity upon planktonic organisms with mainly bacteriostatic activity on biofilms grown on a wound model.

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