Antibacterial Activity of Potential Essential Oil Extracts against the American Foulbrood, Paenibacillus larvae larvae

Abstract

The present study was conducted to investigate the antibacterial activity of potential essential oils at five concentrations (100, 50, 25, 12.5 and 6.25 %) against Paenibacillus larvae larvae (the causative agent of AFB). Different parts of ten plants belong to four families, Rutaceae, Myrtaceae, Anacardiaceae and Lamiaceae were used in present experiment to extract fifteen essential oils. The efficiencies, in inhibition the growth of P. l. larvae bacteria, of these crude oils and four mixtures of some of them beside their diluents were evaluated using disk diffusion assay. Obtained results indicated that the efficiencies, in inhibiting P. l. larvae growth, of Citrus limon essential oil from leaves, peels and mixture of them (at tested concentrations) varied from weak to very high. The most effective one was the crude oil of leaves with inhibition zone of 34.2 mm with 213.5 % relative efficiency (R.E.) of Tylosine. Considering the four plants belonging to Family Lamiaceae, results emphasized the high efficiency of the crude essential oil from Thymus vulgaris whole plant, beside its tested diluents, in inhibiting the growth of P. l. larvae. It was most the effective treatment achieving inhibitory activity (inhibition zone of 47.5 mm) with 245.5 % R.E. Moreover, the same trend was observed when the concentration decreased to be 50, 25 or 12.5 %, which still exhibiting high activities (inhibition zones of 36.3, 33.5 and 30.5 mm with 198.4, 178.3 and 163.4 % R.E., respectively). In general, the antibacterial activities of the evaluated essential oils were concentration-dependent.