Antimicrobial activity of tea tree oil nanoparticles against American and European foulbrood diseases agents

Abstract

Paenibacillus larvae and Melissococcus plutonius are the primary bacterial pathogens of honeybees and the causative agents of American and European foulbrood disease (AFB and EFB) respectively. Such diseases have been gaining importance since there are few therapeutic options beyond the reporting of microorganisms resistant to conventional antibiotics. Due to the inefficiency and/or low efficacy of some antibiotics, researches with nanotechnology represent, possibly, new therapeutic strategies. Nanostructured drugs have presented some advantages over the conventional medicines, such as slow, gradual and controlled release, increased bioavailability, and reduced side-effects, among others. In this study, in vitro antimicrobial activity of tea tree oil (TTO) nanoparticles against Paenibacillus species, including P. larvae and M. plutonius strains was evaluated. Minimal inhibitory concentration (MIC) in Mueller–Hinton or KSBHI broth by the microdilution method was assessed. TTO registered MIC values of 0.18–6.25%, while the MIC values obtained for the TTO nanoparticle were of 0.01–0.93%. The possible toxic effect of TTO and TTO nanoparticle has been assessed by the spraying application method in the concentrations higher than the MICs. Bee mortality was evident only in treatment with TTO and the TTO nanoparticles show no toxic effects after 7days of observation. Our results showed for the first time that TTO nanoencapsulation presented a high activity against Paenibacillus species and M. plutonius strains showing that the use of nanotechnology may represent one alternative way for the treatment or prevention of AFB and EFB.