European foulbrood in honey bees

European foulbrood (EFB) is a severe bacterial brood disease caused by the Gram-positive bacterium Melissocccus plutonius. The disease has a worldwide distribution and is an increasing problem in some areas. Although the causative agent of EFB was described almost a century ago, many basic aspects of its pathogenesis are still unknown. This review presents both historical results and recent molecular data to synthesize present knowledge of this enigmatic honey bee disease.