Antimicrobial activity of essential oils against Paenibacillus larvae
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abstract
American foulbrood is a serious bacterial disease that affects Apis mellifera colonies;
the causative agent is Paenibacillus larvae [1 ]. The aim of the study was to evaluate in
vitro the antimicrobial activity of 32 essential oils against P. larvae. Oils from 21 botanical
species were analyzed by gas chromatography (CG and CG/EM). All essential oils were
classified according to the composition of their main components in two groups: benzene
ring compounds (BRC) and terpene compounds (TC). Minimal inhibitory concentration
(MIC) in MYT broth [2] was assessed by the microdilution method. Final serial dilution
concentrations of the essential oils ranged between 2,000-12.5 mgll. The bacterial
isolates were collected from different Argentina's region. The chromatographic analysis
showed that a 67% of the essential oils contained predominately terpene compounds.
while the remaining 33% included mainly compounds with benzene rings. From the TC
group, Cymbopogon citratus essential oil showed the better antimicrobial activity against
P. larvae with MIC values between 150 and 250 mgl l. The essential oi ls from Aloysia
polystachya and Mentha spp. had the lowest inhibitory activity. Among the oils from the
BRC group, one of the lowest MIC values was found with cinnamon essential oil
(Cinnamomun zeylanicum) being between 25 and 50 mg/L; Origanum vulgare showed the
highest MIC values (350-400 mg/L). Essential oils, especially those with BRC in their
composition, presented inhibitory capacity against P. larvae strains.
