Flagella-Mediated Biofilm Formation and 3D Swarming Drive Virulence in the Honey Bee Pathogen Paenibacillus larvae.

Peritrichous flagella are a key virulence factor in the ERIC II genotype of Paenibacillus larvae, and flagella loss disrupts biofilm formation and 3D swarming linked to infection outcomes.

• Why it matters: American foulbrood threatens honey bee health, yet the specific virulence determinants that enable P. larvae to colonize and invade larvae remain insufficiently defined.
• What they did: The study identified peritrichous flagella in the ERIC II genotype, created a flagella-deficient mutant, and assessed in vitro biofilm traits plus honey bee larva survival with FISH of infected midguts.
• The result: In honey bee larvae, flagella are crucial for biofilm formation on the larval midgut epithelium and for three-dimensional swarming during epithelial invasion, supporting a virulence role for flagella-mediated colonization.

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