Activity of essential oils in vapour phase against Paenibacillus larvae

Abstract

Paenibacillus larvae subspecies larvae, a Gram-positive, spore-forming bacterium, is the causative agent of the American foulbrood (AFB), one of the most serious and destructive brood diseases of honeybees. AFB is a problem for beekeepers world-wide [1]. Thus, in this study we have tested eight essential oils from aromatic plants against two strains of P. larvae, one wild strain isolated from infected honeybee colony (15/08f4) and one standard strain (ATCC 9545). For the tests we have used disc volatilization method, as the application of chemicals in vapour phase in the beehives is simple and common. In addition, several products containing thymol against parasitic mite Varroa destructor are commercially available. Four essential oils were active in the range of tested concentrations (from 1 to 256 nl/ml). The most active was EO from Armoracia rusticana (MICs 16 nl/ml) followed by Thymus vulgaris (MIC 64 nl/ml), Mentha spicata var. crispa (MICs 64 and 128 nl/l against wild and standard strain, respectively) and Satureja hortensis (MICs 128 and 256 nl/ml, respectively). The results are quite promising, the toxicity of active EO against honeybees and possible organoleptic changes of bee products will be checked in the next phase.