Paenibacillus larvae

Paenibacillus larvae is a species of bacterium, found worldwide, which causes American foulbrood, a fatal disease of the larvae of honeybees ("Apis mellifera"). It is a Gram-positive, rod-shaped bacterium, which forms spores which can remain viable for at least thirty-five years.
Morphology.
"P. larvae" is a rod-shaped bacterium with slightly rounded ends, approximately 2.5–5 μm long and 0.5 μm wide. The spore of "P. larvae" is oval, approximately 0.6 μm wide and 1.3 μm long.
Classification.
In 1906, G.F. White first described the bacteria which caused American foulbrood, and named it "Bacillus larvae". In 1950, a bacteria isolated from bee larvae and associated with the rare disease "powdery scale" was named "Bacillus pulvifaciens" by Katznelson. In 1993, both "B. larvae" and "B. pulvifaciens" were transferred to a new genus, "Paenibacillus". The two species were combined into a single species: "Paenibacillus larvae" in 1996, remaining differentiated as two subspecies: "P. larvae" ssp. "larvae" (formerly "Bacillus larvae") and "P. larvae" ssp. "pulvifaciens" (formerly "Bacillus pulvifaciens"). In 2006, the subspecies were eliminated based on spore morphology, biochemical profile and DNA testing, and when it was also demonstrated that experimental infection of honeybee larvae with the "pulvifaciens" subspecies caused American foulbrood signs without causing "powdery scale". 
There are four strains of "P. larvae", named after their enterobacterial repetitive intergenic consensus (ERIC) sequences. Strains I and II correspond to the former species of "Bacillus larvae", and strains III and IV correspond to the former species of "B. pulvifaciens". 
Epidemiology.
"P. larvae" is found worldwide. Strain ERIC I is found worldwide, whereas ERIC II is found only in Europe. Strains ERIC III and IV are found in bacteriology archives and are considered practically unimportant.
American foulbrood.
"P. larvae" causes American foulbrood in honeybees. The most virulent strain of "P. larvae" is ERIC II, which can cause the death of all larvae in a hive within 7 days of infecting the colony.