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Published on: April 25, 2025
Antibacterial activity of varying UMF-graded Manuka honeys
Alodia Girma1, Wonjae Seo1, Rosemary C She1
1Department of Pathology, Keck School of Medicine of the University of Southern California, Los Angeles, California, United States of America.
Abstract:
Honey has been used as a traditional remedy for skin and soft tissue infections due to its ability to promote wound healing. Manuka honey is recognized for its unusually abundant content of the antibacterial compound, methylglyoxal (MGO). The Unique Manuka Factor (UMF) grading system reflects the MGO concentration in Manuka honey sold commercially. Our objective was to observe if UMF values correlated with the antibacterial activity of Manuka honey against a variety of pathogens purchased over the counter. The antibacterial effect of Manuka honey with UMF values of 5+, 10+, and 15+ from the same manufacturer was assessed by the broth microdilution method. Minimum inhibitory concentration (MIC) values were determined against 128 isolates from wound cultures representing gram-positive, gram-negative, drug-susceptible, and multi-drug resistant (MDR) organisms. Lower MICs were observed with UMF 5+ honey for staphylococci (n = 73, including 25 methicillin-resistant S. aureus) and Pseudomonas aeruginosa (n = 22, including 10 MDR) compared to UMF 10+ honey (p<0.05) and with UMF 10+ compared to UMF 15+ (p = 0.01). For Enterobacteriaceae (n = 33, including 14 MDR), MIC values were significantly lower for UMF 5+ or UMF 10+ compared to UMF 15+ honey (p<0.01). MIC50 for UMF 5+, UMF 10+, and UMF 15+ honey against staphylococci was 6%, 7%, and 15%, and for Enterobacteriaceae was 21%, 21%, and 27%, respectively. For Pseudomonas aeruginosa MIC50 was 21% and MIC90 was 21-27% for all UMFs. Manuka honey exhibited antimicrobial activity against a spectrum of organisms including those with multi-drug resistance, with more potent activity overall against gram-positive than gram-negative bacteria. Manuka honey with lower UMF values, in our limited sampling, paradoxically demonstrated increased antimicrobial activity among the limited samples tested, presumably due to changes in MGO content of honey over time. The UMF value by itself may not be a reliable indicator of antibacterial effect.
Insights
Manuka honey shows antibacterial activity against wound pathogens, including multi-drug resistant strains. Lower Unique Manuka Factor (UMF) grades unexpectedly demonstrated stronger antimicrobial effects in this study, suggesting UMF may not reliably indicate antibacterial potency.
Area of Science:
- Microbiology
- Biochemistry
- Wound Healing Research
Background:
- Honey, particularly Manuka honey, is traditionally used for wound healing due to its antimicrobial properties.
- Methylglyoxal (MGO) is the primary antibacterial compound in Manuka honey.
- The Unique Manuka Factor (UMF) grading system quantifies MGO concentration in commercial Manuka honey.
Purpose of the Study:
- To investigate the correlation between Unique Manuka Factor (UMF) values and the in vitro antibacterial activity of Manuka honey.
- To assess the efficacy of Manuka honey against a diverse range of wound pathogens, including drug-susceptible and multi-drug resistant (MDR) organisms.
Main Methods:
- The broth microdilution method was employed to determine the Minimum Inhibitory Concentration (MIC) of Manuka honey.
- Antibacterial activity was tested against 128 isolates from wound cultures, encompassing Gram-positive, Gram-negative, and MDR bacteria.
- Manuka honey samples with UMF 5+, 10+, and 15+ from a single manufacturer were utilized.
Main Results:
- Manuka honey demonstrated antimicrobial activity against all tested organisms, with greater potency against Gram-positive bacteria.
- Lower UMF values (5+ and 10+) showed significantly lower MICs against staphylococci and Pseudomonas aeruginosa compared to higher UMF values (10+ and 15+).
- For Enterobacteriaceae, UMF 5+ and 10+ honey exhibited significantly lower MICs than UMF 15+ honey.
Conclusions:
- Manuka honey possesses broad-spectrum antimicrobial activity, effective even against multi-drug resistant wound pathogens.
- The UMF grading system may not be a definitive indicator of Manuka honey's antibacterial potency, as lower UMF values showed enhanced activity in this study.
- Variations in MGO content over time could explain the paradoxical findings, highlighting the need for further research into honey stability and antibacterial efficacy.
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