34th Annual Scientific Meeting proceedings

Objectives:

Both in human and veterinary medicine, Manuka honey (MH) has received attention due to its antibacterial and wound healing effect. Unlike traditional antimicrobials, resistance to MH has not yet been reported. In human ophthalmology, honey has shown to accelerate corneal wound healing, which substantiates its potential use in corneal ulcerative disease. In this study we tested the antibacterial properties of MH against clinical isolates from equine keratitis, and the effect of MH in combination with commonly prescribed topical antibiotic agents.

Methods:

The Minimum Inhibitory Concentration (MIC) and minimum bactericidal concentrations of MH were determined for eight clinical isolates with microdilution assays and spectrophotometric analyses. To investigate potential synergistic and antagonistic effects, the inhibition of several antibiotics was compared with and without a subinhibitory dose of MH using disk diffusion and E-test strips.

Results:

The spectrophotometric MIC of MH was 12% for all isolates tested, and MH showed a bactericidal effect in high concentrations for all but one isolate. For Staphylococci spp. (including methicillin resistant staphylococci) tetracycline, chloramphenicol and fusidic acid showed an additive effect with MH. An inhibitory effect was observed for ofloxacin and MH, in staphylococci and streptococci. No effect of MH was seen in combination with gentamicin and tobramycin.

Conclusions:

MH shows in vitro inhibitory and bactericidal activity activities against all tested ocular pathogens, including multiresistant isolates. Therefore, MH shows potential for the topical treatment of equine infectious keratitis. Careful consideration should be taken when combining MH with topical antibiotic agents, as both possible enhanced and diminished effects were observed.