Efficacy of indigenous plant essential oil Andean thyme (Acantholippia seriphioides A. Gray) to control American foulbrood (AFB) in honey bee (Apis mellifera L.) hives.

Headspace volatiles of an oil of an autochthonous Argentinean plant, Andean thyme (Acantholippia seriphioides A. Gray) and its in vitro antimicrobial activity against thirteen strains of Paenibacillus larvae, causal agent of American foulbrood (AFB), was determined. This disease affects honey bees (Apis mellifera L.) colonies worldwide causing great economical loses. The antimicrobial activity of the essential oil was evaluated using the broth microdilution method. Seven compounds representing 93.1% of the total of this oil were identified in the headspace of the oil using SPME-GC/MS analysis. The main components were thymol (29.2%), p-cymene (23.3%), carvacrol (23.3%) and γ-terpinene (11.0%). One way ANOVA for minimum inhibitory concentration (MIC) data and minimal bactericide concentration (MBC) data, indicated highly significant differences between the P. larvae strains. Newman-Keuls test determined two homogeneous groups (α=0.05) corresponding to Argentinian and Italian strains with different responses to Andean thyme oil. The use of essential oils in the control of microbial strains allows an alternative scope for the control of this serious disease affecting honey and its by-products (wax, pollen and propolis). Such strategy can meet consumer demand for a diminution or absence of other antimicrobial chemical substances, which can be substituted by the addition of natural substances