The main goal of the current study was
to assess the effect of the oral administration of the metabolites produced by Lactobacillus
johnsonii CRL1647 (mainly organic acids) supplemented in syrup, on: (I) N. ceranae
sporulation dynamics before and after fumagillin application, and (II) performance of A.
mellifera colonies. Different experiments were conducted to evaluate the effects of these
bacterial metabolites on bees: in vitro administration revealed no toxic effects against
bees.