Tyramine is not essential for European foulbrood pathogenesis in a virulent Melissococcus plutonius strain

Area of Science:

• Apiculture
• Microbiology
• Insect Pathology

Background:

• European foulbrood is a significant bacterial disease impacting honey bee brood.
• Highly virulent clonal complex 12 (CC12) strains of Melissococcus plutonius cause this disease, but their virulence factors are not fully understood.
• Tyramine has been investigated as a potential virulence factor.

Purpose of the Study:

• To investigate the role of tyramine production in the pathogenicity of CC12 strains of Melissococcus plutonius.
• To determine if the tyrosine decarboxylase gene (tdc) is responsible for tyramine production in these bacteria.

Main Methods:

• Construction of a knockout mutant for the putative tyrosine decarboxylase gene (tdc) in a CC12 strain.
• Confirmation of the mutant's inability to produce tyramine.
• Assessment of the virulence of the tdc knockout mutant in honey bee brood.

Main Results:

• The tdc knockout mutant successfully lost the ability to produce tyramine.
• The mutant strain exhibited no significant attenuation in virulence compared to the wild-type strain.
• These findings indicate that tyramine production is not a critical factor for CC12 strain pathogenicity.

Conclusions:

• Tyramine production mediated by the tdc gene is not essential for the virulence of Melissococcus plutonius CC12 strains.
• The study suggests that other virulence factors are likely responsible for the pathogenicity of these strains in European foulbrood.