American foulbrood is an animal disease that can destroy entire colonies of bees. The pathogenic agent of this notifiable animal disease is the bacterium Paenibacillus larvae (P. larvae). Larvae that are supposed to grow into bees are decomposed into a slimy, stringy mass. The brood, and often the whole colony, must be destroyed to eliminate the epidemic.

Several years ago Dr. Elke Genersch was able to demonstrate that there are genetically distinct types of P. larvae. Two of them are responsible for the destruction of beehives worldwide: ERIC I and ERIC II. One obvious difference between the two genotypes is the course taken by the disease: ERIC II kills the larvae faster than ERIC I. Genersch and her team hope to find out why this is so as they continue their DFG project on the molecular pathogenesis of American foulbrood.

In 2008 Dr. Elke Genersch and her research team discovered the infection mechanism of the deadly bee disease: the pathogen populates the midgut of the larva and lives from the food ingested by the larva. Once the larval gut is filled to the point of bursting, the bacteria break through the intestinal wall and enter the surrounding tissue. The ERIC I bacterium penetrates through the intestinal wall with the help of toxins. ERIC II has developed a different mechanism: it forms a so-called surface-layer protein on its cell surface, which it uses to attach itself to the intestinal cells of the larva, where it destroys the connections between the epithelial cells.

In order to understand the pathogenesis of this deadly disease, Genersch aims to identify other factors that make the bacterium so dangerous and cause the difference in virulence in the bacteria. She also plans to explore where the bacterium comes from and how it is spread.