The gram-positive bacterium Melissococcus plutonius is the primary pathogen of European foulbrood (EFB) in bees. It mainly affects so-called coiled larvae, which then die at 4 – 5 days of age. The larvae are infected through the food and the pathogen multiplies in the gut. Infected brood changes colour and becomes a semi-liquid mass, which later on dries out to loose scales. Due to the partly sour smell, it is also referred to as sourbrood. After capping, the caps are sunken and perforated. The signs are very similar to those of American foulbrood, a disease which is notifiable upon suspicion in Germany, thus, a precise diagnosis is of great importance. Transmission can either occur through the bees themselves (drifting, robbing) or by the beekeeper. By forming an artificial swarm, the brood can be separated from the healthy bees and then killed.