A 2025 study found that 12% manuka honey effectively inhibits bacterial growth associated with equine ulcerative keratitis, though low concentrations may enhance some pathogens.
Manuka honey demonstrated strong antibacterial properties against multi-resistant bacteria causing equine ulcerative keratitis in a 2025 in vitro study, according to research cited by Equimanagement. The study, published in Veterinary Ophthalmology, found that a 12% manuka honey solution inhibited growth of bacteria commonly found in equine ulcerative keratitis, regardless of their antimicrobial resistance profile. A study conducted by researchers from Utrecht University in the Netherlands examined the antibacterial effects of manuka honey, both in combination with and separately from antibiotics typically used for treating ulcerative keratitis in horses.
Concentration Matters for Efficacy
While 12% manuka honey showed consistent antibacterial activity, lower concentrations yielded mixed results. The research observed that at low concentrations of manuka honey (4%), bacterial growth appeared to be stimulated, particularly in the case of Streptococcus species. Researchers emphasized that tear film dilution could reduce honey’s effectiveness, urging further research to determine optimal concentrations for clinical use. The study also discovered that manuka honey exhibited bactericidal effects at concentrations ranging from 8-28% against a methicillin-resistant coagulase-negative Staphylococcus (S. sciuri).
Antibiotic Combinations Show Promise
Combining 5% manuka honey with certain antibiotics improved antibacterial effects. The research demonstrated that combining 5% manuka honey with tetracycline, chloramphenicol, or fusidic acid improved the antibacterial efficacy against Staphylococcus species (including methicillin-resistant strains). However, the antibacterial impact of ofloxacin and cloxacillin was slightly diminished when paired with 5% manuka honey in some but not all bacterial cases. The researchers saw no effects from combining manuka honey with gentamicin or tobramycin. These findings were part of an in vitro study on bacterial isolates, where the minimal inhibitory concentration of manuka honey was 12% for all tested bacteria.
Clinical Application Challenges
While manuka honey’s antibacterial properties are promising, the study highlighted potential hurdles. Researchers noted that low concentrations of manuka honey could potentially be counterproductive, and clinical studies would be helpful to determine if the equine eye tolerates manuka honey application. The study also noted that in humans, initial application can cause transient ocular stinging. The researchers concluded that manuka honey exhibits inhibitory and bactericidal properties against multi-resistant bacteria frequently encountered in equine corneal disease, stating, a solution of 12% manuka honey effectively inhibited the growth of bacteria commonly found in equine ulcerative keratitis, regardless of their antimicrobial resistance profile.
The study, titled In Vitro Activity of Manuka Honey, Either Alone or in Combination With Topical Antibiotics, Against Bacteria Commonly Found in Equine Ulcerative Keratitis, was published in Veterinary Ophthalmology in November 2025 with DOI 10.1111/vop.70111. Researchers Barvelink M, Brok B, Djajadiningrat-Laanen SC, et al., authored the work. The study’s findings underscore the potential of manuka honey as a potential topical drug to treat infectious keratitis.