''Paenibacillus larvae'' are a species of bacterium, found worldwide, which cause

American foulbrood American foulbrood (AFB, ''Histolysis infectiosa perniciosa larvae apium'', ''Pestis americana larvae apium''), caused by the Endospore, spore-forming bacterium ''Paenibacillus larvae'', is a highly infectious honey bee brood disease. It is the ...

, a fatal disease of the larvae of honeybees (''

Apis mellifera The western honey bee or European honey bee (''Apis mellifera'') is the most common of the 7–12 species of honey bees worldwide. The genus name ''Apis'' is Latin for 'bee', and ''mellifera'' is the Latin for 'honey-bearing' or 'honey-carrying', ...

''). It is a

Gram-positive In bacteriology, gram-positive bacteria are bacteria that give a positive result in the Gram stain test, which is traditionally used to quickly classify bacteria into two broad categories according to their type of cell wall. The Gram stain is ...

, 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 bacterium that caused American foulbrood (AFB), and named it ''Bacillus larvae''. In 1950, a bacterium 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 at least four

genotype The genotype of an organism is its complete set of genetic material. Genotype can also be used to refer to the alleles or variants an individual carries in a particular gene or genetic location. The number of alleles an individual can have in a ...

s of ''P. larvae'', named after their enterobacterial repetitive intergenic consensus (ERIC) sequences. Genotype ERIC I corresponds to the former species of ''Bacillus larvae'', and genotypes ERIC II, III and IV correspond to the former species of ''B. pulvifaciens''. A fifth genotype ERIC V has recently been discovered in honey.

Epidemiology

''P. larvae'' is found worldwide. Genotypes ERIC I and II are most frequently isolated from global AFB outbreaks. In contrast, genotypes ERIC III and IV are found in bacteriology archives and are considered practically unimportant. ERIC V was found in honey and has not been isolated from infected colonies yet.

American foulbrood

''P. larvae'' causes American foulbrood in honeybees. The transmission is helped by

small hive beetle ''Aethina tumida,'' commonly known as small hive beetle (SHB), is a beekeeping pest. It is native to sub-Saharan Africa, but has spread to many other regions, including North America, Australia, and the Philippines. The small hive beetle primar ...

, which the infected small hive beetle can spread the bacteria by directly contacting both honey and honeybee.

References

{{Authority control Paenibacillaceae Bee diseases