How methylglyoxal kills bacteria: An ultrastructural study.
Antibacterial activity of honey is due to the presence of methylglyoxal (MGO), H2O2, bee defensin as well
as polyphenols. High MGO levels in manuka honey are the main source of antibacterial activity. Manuka
honey has been reported to reduce the swarming and swimming motility of Pseudomonas aeruginosa
due to de-flagellation. Due to the complexity of honey it is unknown if this effect is directly due to MGO.
In this ultrastructural investigation the effects of MGO on the morphology of bacteria and specifically the
structure of fimbriae and flagella were investigated. MGO effectively inhibited Gram positive (Bacillus
subtilis; MIC 0.8 mM and Staphylococcus aureus; MIC 1.2 mM) and Gram negative (P. aeruginosa; MIC 1.0
mM and Escherichia coli; MIC 1.2 mM) bacteria growth. The ultrastructural effects of 0.5, 1.0 and 2 mM
MGO on B. substilis and E. coli morphology was then evaluated. At 0.5 mM MGO, bacteria structure was
unaltered. For both bacteria at 1 mM MGO fewer fimbriae were present and the flagella were less or
absent. Identified structures appeared stunted and fragile. At 2 mM MGO fimbriae and flagella were
absent while the bacteria were rounded with shrinkage and loss of membrane integrity. Antibacterial
MGO causes alterations in the structure of bacterial fimbriae and flagella which would limit bacteria
adherence and motility.