* Caused by: Melissococcus pluton * non spore-forming bacterium * brood disease * stress disease European Foulbrood (EFB) is a bacterial brood disease, caused by the bacterium Melissococcus pluton. This disease is considered a stress disease and is most prevalent in spring and early summer. Melissococcus pluton does not form spores, but the organism often over-winters on combs. It gains entry into the larva in contaminated brood food and multiplies rapidly within the gut of the larva. European foulbrood frequently disappears with a nectar flow. Occasionally the disease remains active throughout the entire foraging season. All castes of bees are susceptible, although various commercial strains differ in susceptibility.