Abstract
BackgroundHoney has previously been shown to have wound healing and antimicrobial properties, but this is dependent on the type of honey, geographical location and flower from which the final product is derived. We tested the antimicrobial activity of a Chilean honey made by Apis mellifera (honeybee) originating from the Ulmo tree (Eucryphia cordifolia), against selected strains of bacteria.MethodsUlmo 90 honey was compared with manuka UMF® 25+ (Comvita®) honey and a laboratory synthesised (artificial) honey. An agar well diffusion assay and a 96 well minimum inhibitory concentration (MIC) spectrophotometric-based assay were used to assess antimicrobial activity against five strains of methicillin-resistant Staphylococcus aureus (MRSA), Escherichia coli and Pseudomonas aeruginosa.ResultsInitial screening with the agar diffusion assay demonstrated that Ulmo 90 honey had greater antibacterial activity against all MRSA isolates tested than manuka honey and similar activity against E. coli and P. aeruginosa. The MIC assay, showed that a lower MIC was observed with Ulmo 90 honey (3.1% - 6.3% v/v) than with manuka honey (12.5% v/v) for all five MRSA isolates. For the E. coli and Pseudomonas strains equivalent MICs were observed (12.5% v/v). The MIC for artificial honey was 50% v/v. The minimum bactericidal concentration for all isolates tested for Ulmo 90 honey was identical to the MIC. Unlike manuka honey, Ulmo 90 honey activity is largely due to hydrogen peroxide production.ConclusionsDue to its high antimicrobial activity, Ulmo 90 may warrant further investigation as a possible alternative therapy for wound healing.
Highlights
Honey has previously been shown to have wound healing and antimicrobial properties, but this is dependent on the type of honey, geographical location and flower from which the final product is derived
To date there are many publications reporting both in vitro and in vivo on the therapeutic properties of manuka honey, which have confirmed its activity against a wide range of medically important bacteria including methicillin-resistant Staphylococcus aureus (MRSA) [4,5]
Initial screening with the agar diffusion assay demonstrated that Ulmo 90 honey had superior antibacterial activity against all isolates compared with manuka honey
Summary
Bacterial Strains The antibacterial properties of three honeys were tested against seven bacterial isolates, i.e. three reference strains, Escherichia coli ATCC 35218, Pseudomonas aeruginosa ATCC 27853 and MRSA ATCC 43300 and four MRSA clinical isolates (two nasal, 01322 and 00745 and two surgical site/wound isolates, 00791 and 28965, from patients in an Irish hospital). A serial double dilution of honey (Ulmo, manuka or laboratory honey) was prepared aseptically for use in both the agar well diffusion and MIC assay from 50% to 0.02% v/v in nutrient broth (Oxoid, Fannin, Ireland). To establish if the antibacterial activity of the three honey samples was bacteriostatic or bactericidal [11], 10 μl from a well with each concentration of honey where bacterial growth was inhibited, were plated on to Colombia Blood Agar (CBA) (Oxoid) and incubated overnight. Hydrogen peroxide activity of honey In order to determine if each of the honeys (Ulmo 90 and manuka) had non-peroxide antimicrobial activity, honey dilutions (50% - 1.6% v/v) were prepared in nutrient broth containing catalase (Sigma, C-40) at a final concentration of 0.2% w/v [12]. Plates were incubated at 37° C for 24 h and subsequently examined for growth
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