Characterization of volatile constituents from Origanum onites and their antifungal and antibacterial activity.
2013
Essential oils obtained by hydrodistillation (HD)
and microwave-assisted HD (MWHD) of Origanum
onites aerial parts were analyzed by GC and
GC/MS. Thirty-one constituents representing
98.6% of the water-distilled oil and 52 constituents
representing 99.6% of the microwave-distilled oil
were identified. Carvacrol (76.8% HD and 79.2%
MWHD) and thymol (4.7% HD and 4.4% MWHD)
were characterized as major constituents in both
essential oils. Separation of carvacrol and thymol was
achieved by overpressured layer chromatography.
HPTLC and TLC separations were also compared.
Essential oils were evaluated for antifungal activity
against the strawberry anthracnose-causing
fungal plant pathogens Colletotrichum acutatum,
C. fragariae, and C. gloeosporioides using a direct
overlay bioautography assay. Furthermore, main
oil components carvacrol and thymol were then
evaluated for antifungal activity; only carvacrol
demonstrated nonselective antifungal activity
against the three Colletotrichum species. Thymol
and carvacrol were subsequently evaluated
in a 96-well microdilution broth assay against
Phomopsis obscurans, Fusarium oxysporum,
three Colletotrichum species, and Botrytis cinerea. No activity was observed against any of the three
Colletotrichum species at or below 30 μM. However,
thymol demonstrated antifungal activity and produced
31.7% growth inhibition of P. obscurans at 120 h
and 0.3 μM, whereas carvacrol appeared inactive.
Thymol and carvacrol at 30 μM showed 51.5 and
36.9% growth inhibition of B. cinerea at 72 h. The
mechanism of antibacterial activity was studied in
a bioautography-based BioArena system. Thymol
and carvacrol showed similar inhibition/killing effectagainst Bacillus subtilis soil bacteria; the action could be enhanced by the formaldehyde generator and
transporter copper(II) ions and could be decreased in
the presence of L-arginine, a formaldehyde capturer.
Results indicated that Origanum essential oils and its
major components thymol and carvacrol appear to
generate antimicrobial activity through a mechanism
of action where formaldehyde and its reaction
products are produced.
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