Résumé
This work considered the widespread of European foulbrood [EFB] infections among honeybee colonies in Egypt. Apiaries in some Egyptian-Delta governorates were inspected for the occurrence of foulbrood during the period extended from February 2007 to June 2008. Field diagnosis illustrated the abundance of EFB-symptoms among the inspected apiaries in spring and early summer as well as in winter. Investigation of foulbrood-associated-microflora revealed the dominance of Gram-positive non spore-forming cocci-shaped bacteria followed by Gram-positive aerobic spore-forming bacilli. Isolation and identification of Melissococcus pluton from scales verified the preliminary field diagnosis of foulbrood type. According to some of their morphological, cultural and biochemical characteristics 97 of cocci-shaped isolates were belonged to M. pluton, the primary aetiological EFB agent, and 91 strains were related to the secondary EFB invading bacterium Streptococcus faecalis. Characterization of spore-forming bacilli isolated from EFB affected larvae indicated the absence of Paenibacillus larvae, the American foulbrood causing agent, and the dominance of Paenibacillus alvae, the second EFB indicator. This conclusively confirmed the field diagnosis of EFB clinical symptoms as well as the preliminary detection of EFB causing bacterium in the laboratory. Essential oils from Eucalyptus globules, Coriandrum sativum, Citrus nobilis, Citrus limonum and Thymus vulgaris exhibited in vitro various antibacterial activities against M. pluton. Eucalyptus globules oil was the most effective antibacterial substance against the pathogen; growth inhibition due to this phytochemical was a concentration dependent trait