European foulbrood in Czechia after 40 years: application of next-generation sequencing to analyze Melissococcus plutonius transmission and influence on the bacteriome of Apis mellifera

Worker honeybees (Apis mellifera) transmit Melissococcus plutonius between colonies. However, the transmission of M. plutonius, which causes European foulbrood (EFB), is poorly understood. To analyze the first EFB outbreak in 40 years in Czechia, we collected 49 hive worker samples from 18 beehives in two diseased apiaries for bacteriome analysis of the V1-V3 portion of the 16S rRNA gene. When we compared control samples obtained outside of the EFB zone, bees from an EFB apiaries containing colonies without clinical symptoms and bees from colonies with EFB clinical symptoms, there was a 100-fold higher occurrence of M. plutonius in colonies with EFB symptoms. The presence of M. plutonius in controls indicated that this pathogen exists in an enzootic state. EFB influenced the core bacteria in the worker bacteriome because the number of Snodgrassella alvi, Lactobacillus mellis, Lactobacillus melliventris, and Fructobacillus fructosus sequences increased, while Bartonella apis, Frischella perrara, and Commensalibacter intestine sequences decreased. Together, the results of this study suggest worker bees from EFB-diseased apiaries serve as vectors of M. plutonius, and eliminating such colonies is an appropriate method to overcome disease outbreaks. Because M. plutonius exists in honeybee colonies in an enzootic state, there may be similar abundances in control colonies outside the EFB zone to those in asymptomatic colonies from EFB apiaries. High-throughput Illumina next-generation sequencing permitted the quantitative interpretation of M. plutonius within the honeybee worker bacteriome. Future studies focusing on honeybee diseases, colony losses, detection of bacterial pathogens and interactions of bacteriome with pathogenic bacteria will benefit of this study.