Absence of bacterial resistance to medical-grade manuka honey

Abstract

were exposed to sub-lethal concentrations of manuka honey in continuous and stepwise training experiments to determine whether susceptibility to honey diminished. Reduced susceptibilities to manuka honey in the test organisms during long-term stepwise resistance training were found, but these changes were not permanent and honey-resistant mutants were not detected. The risk of bacteria acquiring resistance to honey will be low if high concentrations are maintained clinically.Response to Reviewers: Dear Editor, Thank you for the reviewers' comments on our paper entitled "Absence of bacterial resistance to medical-grade manuka honey". We were pleased that they liked the design and execution of our study and we understood the reservations that reviewer had about our conclusions. We have made the following changes in response to each specific observation, which we feel strengthen our paper: Reviewer 1. We have inserted line numbers into the paper. In order to rebut the reservations about our conclusions we have recently performed further tests on the four clinical isolates that were collected at the end of the recovery period and stored at -80⁰C. For each of the thawed cultures, MICs and MBCs were determined in duplicate on three separate occasions. We found that three cultures (P.aeruginosa, S. epidermidis and MRSA) had returned to pre-training levels of susceptibility and that the MIC of E. coli was only 1.4 times higher than at time 0. That information is included as Table 2 (line 370) and described in lines 201 to 209. We respectfully maintain that honey-resistant mutants were not recovered. To support this conclusion as advised we noted (lines 241-243) that antibiotic-resistance training led to MICs that increased by factors of either 32 or 64 (citation 17-Blair et al, 2009), while honey resistance training led to an increase of 1.4. We also used the EUCAST definition of clinical resistance to show that honey susceptibility which had increased by a factor of 1.4 is unlikely to lead to therapeutic failure when wound care products normally contain at least 80% manuka honey and normally 95%(w/v) (lines 258 to 260). We have removed the statement "gradually increased towards pre-treatment levels". We have made clear the proportional changes in MICs (lines 195 to 197 and 208 and 251). We have commented on the need to maintain high concentrations of manuka honey in wounds to avoid the selection of resistant strains (lines 278 to 284). We have modified the Abstract (lines 42 to 45) to explain that reduced susceptibility was found during long-term training and we have commented on the need to maintain high concentrations of manuka honey during clinical use (lines 45 to 46). In the concluding paragraph we also note that prolonged exposure to antimicrobial agents should be avoided. We have deleted statements about the development of antibiotic resistance from the Introduction and the Discussion. We have inserted "preceding days' culture" into line 169, and "day" into line 194. We have removed the reference to high sugar c...

Manuka honey inhibits the development of Streptococcus pyogenes biofilms and causes reduced expression of two fibronectin binding proteins

“…The dilution of honey does not seem to affect the antimicrobial properties; MGO has been shown to remain active upon dilution but additional undefined factors are believed to maintain cidality when MGO is diluted below 0.53 mg ml 21 (Jervis- Bardy et al, 2011). Unlike systemic antibiotics and other topical antimicrobials, the risk of bacterial resistance to manuka honey was low, even when high usage was maintained and to date, no 'honey-resistant' isolates have been found (Blair et al, 2009;Cooper et al, 2010). Therefore, manuka honey represents an efficacious and safe alternative to failing systemic and topical treatments that are currently used to treat wounds that are infected with S. pyogenes.…”

Colour Intensity, Polyphenol Content and Antibacterial Capacity of Unheated and Heat-Treated Sahara Honey

“…Minimum inhibitory concentration (MIC) was used to determine the lowest concentration of honey-in-water solution (w/v) at which the percentage inhibition is almost 100% [21,22]. The MIC before and after heat-treatment of SH hydrogen peroxide, although involved in antibacterial action [27][28][29][30][31][32].…”

Antimicrobial activity of organic honeys against food pathogenic bacterium Clostridium perfringens

“…Many in vitro studies have shown antimicrobial activity of different honeys against a wide range of skin-colonizing and foodborne bacterial species, including antibiotic-resistant bacteria (Mundo et al 2004;Lusby et al 2005;Lin et al 2009;Kwakman et al 2008Kwakman et al , 2010. It has been shown that also in vivo honey has beneficial actions against wound infections (Robson et al 2009), and licensed honey products are widely used in wound care (Cooper et al 2010). Recently, significant antimicrobial activity of engineered organic honey against wound infections has been reported (Dryden et al 2014).…”