Oral Presentation Australian Society for Microbiology Annual Scientific Meeting 2014

Antimicrobial effects of honey on three problematic bacterial pathogens seen in the horse.  (#129)

Emma M Chandler 1 , Alysia Parnell 1 , Patricia A Martin 1 , Gary Muscatello 1
  1. The University of Sydney, The University Of Sydney, NSW, Australia

Multi-drug resistant bacteria and MRSA are on the increase in equine hospitals, with clinicians continually struggling to successfully treat horses suffering from pseudomoniasis and dermatophilosis due in part to multi-drug resistance and ineffectual topical medications. This study aims to evaluate effects of three grades of Manuka Honey (UMF 20+, 15+ and 10+) and a locally produced honey (Gordon, NSW) on three species associated with problematic infections in the horse, namely MRSA, MDR Pseudomonas aeruginosa and the causative agent of ‘Greasy Heel’ Dermatophilus congolensis. Twenty-two isolates from equine origins comprising of MRSA (n=5), MDR P. aeruginosa (n=5)and D. congolensis (n=12) were evaluated for their susceptibility to honeys using the standard CLSI macrodilution method. Minimum inhibitory concentrations (MIC) and minimum lethal concentration (MLC) were assessed for each isolate. Wilcoxon matched-pair signed-rank test were performed to compare bacteriostatic and bactericidal effects between honeys tested within species.   Generally, MRSA and D. congolensis appeared to be more susceptible to honey then P. aeruginosa. MIC50values ranged from 3% to 6.25% (v/v) for MRSA, 3.125% to 12.5% for D. congolenisis and 11% to 12.5% for P. aeruginosa. Similarly MLC50 values ranged from 3% to 12.5% for MRSA, 3.125% to 12.5% for D. congolenisis and 11% to 25% for P. aeruginosa. There was no difference in antimicrobial effects between grades of Manuka honey, however, bactericidal and bacteriostatic effects of the locally produced honey against D. congolensis was significantly greater than Manuka honeys (P<0.05; MIC50=3.125% compared to 6.25% and MLC50=3.125% compared to 6.25%).The antimicrobial effects of various honeys against these equine bacterial pathogens, opens up the potential application of honey in the topical treatment of ‘Greasy Heel’ and wounds infected with MRSA and/or P. aeuroginosa. The observed differences in susceptibility to honey between pseudomonas, staphylococci and dermatophilus may be relevant in treatment of mixed infections.