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Putative determinants of virulence in Melissococcus plutonius, the bacterial agent causing European foulbrood in
Daniela Grossar1,2, Verena Kilchenmann2, Eva Forsgren3
1Department of Ecology and Evolution, Biophore, UNIL-Sorge, University of Lausanne , Lausanne, Switzerland.
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 co-infection 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.
Insights
Melissococcus plutonius virulence varies among strains, impacting European foulbrood (EFB) in honey bees. Increased virulence is linked to melissotoxin A-carrying plasmids, potentially explaining recent EFB outbreaks.
Area of Science:
- Bacteriology
- Apiculture
- Pathogenomics
Background:
- Melissococcus plutonius causes epidemic European foulbrood (EFB) in honey bees.
- Understanding M. plutonius virulence is crucial for disease control and containment.
Purpose of the Study:
- To investigate the variation in M. plutonius virulence among different isolates.
- To identify factors contributing to virulence differences in M. plutonius.
Main Methods:
- Standardized in vitro assays were used to assess virulence of 16 M. plutonius isolates.
- Multilocus sequence typing and experimental co-infection with Paenibacillus alvei were performed.
- Correlation analysis was conducted between virulence, in vitro growth dynamics, and plasmid presence.
Main Results:
- Significant variation in M. plutonius virulence was observed across isolates from different European countries.
- Virulence was independent of multilocus sequence type and unaffected by co-infection with P. alvei.
- In vitro virulence correlated with growth dynamics and the presence of a plasmid encoding melissotoxin A.
Conclusions:
- Melissococcus plutonius virulence is influenced by mobile genetic elements, specifically plasmids carrying the melissotoxin A gene.
- Acquisition of toxin-carrying plasmids may enhance M. plutonius virulence, potentially contributing to recent EFB outbreaks.
