Paenibacillus larvae

Other Scientific Names

• Paenibacillus larvae subsp. larvae (White 1906)

• Domain: Bacteria
•     Phylum: Bacteroidetes
•         Class: Sphingobacteria
•             Order: Sphingobacteriales
•                 Family: Flexibacteraceae
•                     Genus: Paenibacillus
•                         Species: Paenibacillus larvae

Paenibacillus is a genus of Gram-positive, facultative anaerobic, endospore-forming bacteria. Members of this genus were originally included in Bacillus, until reclassification separated them into a distinct genus in 1993 (Ash et al., 1993).

Paenibacillus larvae causes American foul brood in honeybees (Apis mellifera). Previously, American foul brood and powdery scale disease were considered distinct (Graaf et al., 2006), but this is no longer valid and the pathogenic agents, Paenibacillus larvae subsp. larvae and Paenibacillus larvae subsp. pulvifaciens, were reclassified as one species, Paenibacillus larvae (Genersch et al., 2006), although the subspecies are still referred to in the literature.

P. larvae are Gram-positive, rod-shaped, round-ended and spore-forming bacteria. They are only visible under a high-power microscope. They vary greatly in size, being 0.5 μm wide and between 1.5 and 6 μm long; they occur both singly and in chains and filaments. Some strains are motile. Spores contaminate bee larval food and larvae ingest and become infected by the spores. The spores germinate in the larval gut and the vegetative bacteria are nourished by the larvae. Before the vegetative form of the bacterium dies, millions of spores are produced and can be spread to other bees. (OIE, 2013a; Pennsylvania Department of Agriculture, undated).

Studies have shown geographical clustering of different genotypes. Peters et al. (2006) reported five different genotypes (AB, Ab, ab, aβ and A) in Arnsberg, Germany in studies between March 2003 and October 2004. Two genotypes were found in one hive and it was reported that the five genotypes were not randomly distributed in the district.

American foul brood is a serious disease of honey bees worldwide and causes considerable economic losses (Basualdo et al., 2008). This disease has caused a significant decrease in honeybee populations, beekeeping industries and agricultural production (Antúnez et al., 2010). Honey bees are important to the agricultural and horticultural sectors as pollinators -- the value of pollination is estimated to exceed the value of products from beehives many-fold (Delaplane and Mayer, 2000) -- so any disease causing decline in bee populations will have a significant impact on their role in these industries.

Impact on Habitats

A decline in bee numbers has been attributed to American foul brood, amongst other bee diseases. Bee decline will have a significantly negative affect on pollination within habitats that rely on these insects for development (Delaplane and Mayer, 2000).

Impact on Biodiversity

A decline in native bees due to the spread of American foul brood will have a negative effect on bee biodiversity (Cuthbertson and Brown, 2009).

The effect of American foul brood outbreaks on honeybee health will also have a significant impact on honey products and thus the livelihood of beekeepers.

• Highly mobile locally
• Has high reproductive potential
• Has propagules that can remain viable for more than one year
• Reproduces asexually

• Host damage
• Increases vulnerability to invasions
• Negatively impacts agriculture
• Negatively impacts animal health
• Negatively impacts livelihoods
• Reduced native biodiversity
• Threat to/ loss of native species

• Pathogenic

• Highly likely to be transported internationally accidentally
• Difficult to identify/detect as a commodity contaminant
• Difficult to identify/detect in the field