Skip to main content
Research article - Peer-reviewed, 2020

Putative determinants of virulence in Melissococcus plutonius, the bacterial agent causing European foulbrood in honeybees

Grossar, Daniela; Kilchenmann, Verena; Forsgren, Eva; Charrière, Jean-Daniel ; Gauthier, Laurent; Chapuisat, Michel ; Dietemann, Vincent


Melissococcus plutonius is a bacterial pathogen that causes epidemic outbreaks of European foulbrood (EFB) in honey bee populations. The pathogenicity of a bacterium depends on its virulence, and understanding the mechanisms influencing virulence may allow for improved disease control and containment. Using a standardized in vitro assay, we demonstrate that virulence varies greatly among sixteen M. plutonius isolates from five European countries. Additionally, we explore the causes of this variation. In this study, virulence was independent of the multilocus sequence type of the tested pathogen, and was not affected by experimental coinfection with Paenibacillus alvei, a bacterium often associated with EFB outbreaks. Virulence in vitro was correlated with the growth dynamics of M. plutonius isolates in artificial medium, and with the presence of a plasmid carrying a gene coding for the putative toxin melissotoxin A. Our results suggest that some M. plutonius strains showed an increased virulence due to the acquisition of a toxin-carrying mobile genetic element. We discuss whether strains with increased virulence play a role in recent EFB outbreaks.


European foulbrood; EFB; Melissococcus plutonius; virulence; melissotoxin A; honey bee; Apis mellifera

Published in

2020, volume: 11, number: 1, pages: 554-567

Authors' information

Grossar, Daniela
University of Lausanne
Kilchenmann, Verena
Swiss Bee Research Centre
Swedish University of Agricultural Sciences, Department of Ecology
Charrière, Jean-Daniel
Swiss Bee Research Centre
Gauthier, Laurent
Swiss Bee Research Centre
Chapuisat, Michel
University of Lausanne
Dietemann, Vincent
Swiss Bee Research Centre

UKÄ Subject classification

Microbiology in the medical area

Publication Identifiers


URI (permanent link to this page)