Antibacterial Activity of a Cardanol from Thai Apis
mellifera Propolis
Int J Med Sci, 2014 Feb 7;11(4):327-36
Background: Propolis is a sticky, dark brown resinous
residue made by bees that is derived from plant resins. It is used to construct
and repair the nest, and in addition possesses several diverse bioactivities.
Here, propolis from Apis mellifera from Nan province, Thailand, was tested for
antibacterial activity against Gram(+ve) (Staphylococcus aureus and
Paenibacillus larvae) and Gram(-ve) (Escherichia coli) bacteria.
Materials and methods: The three bacterial isolates were
confirmed for species designation by Gram staining and analysis of the partial
sequence of 16S rDNA. Propolis was sequentially extracted by methanol,
dichloromethane and hexane. The antibacterial activity was determined by agar
well diffusion and microbroth dilution assays using streptomycin as a positive
control. The most active crude extract was further purified by quick column and
adsorption chromatography. The apparent purity of each bioactive fraction was
tested by thin layer chromatography. The chemical structure of the isolated
bioactive compound was analyzed by nuclear magnetic resonance (NMR).
Results: Crude methanol extract of propolis showed the best
antibacterial activity with a minimum inhibition concentration (MIC) value of 5
mg/mL for S. aureus and E. coli and 6.25 mg/mL for P. larvae. After quick
column chromatography, only three active fractions were inhibitory to the
growth of S. aureus and E. coli with MIC values of 6.25 and 31.3 µg/mL,
respectively. Further adsorption chromatography yielded one pure bioactive
fraction (A1A) with an IC50 value of 0.175 µg/mL for E. coli and 0.683 µg/mL
for P. larvae, and was determined to be cardanol by NMR analysis. Scanning and
transmission electron microscopy analysis revealed unusual shaped (especially
in dividing cells), damaged and dead cells in cardanol-treated E. coli.
Conclusion: Thai propolis contains a promising antibacterial
agent.
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