Using whole genome sequencing to study American foulbrood epidemiology in honeybees.

Joakim Ågren,Eva Forsgren,Marc Oliver Schäfer,Wolfgang Blenau

doi:10.1371/journal.pone.0187924

Abstract

American foulbrood (AFB), caused by Paenibacillus larvae, is a devastating disease in honeybees. In most countries, the disease is controlled through compulsory burning of symptomatic colonies causing major economic losses in apiculture. The pathogen is endemic to honeybees world-wide and is readily transmitted via the movement of hive equipment or bees. Molecular epidemiology of AFB currently largely relies on placing isolates in one of four ERIC-genotypes. However, a more powerful alternative is multi-locus sequence typing (MLST) using whole-genome sequencing (WGS), which allows for high-resolution studies of disease outbreaks. To evaluate WGS as a tool for AFB-epidemiology, we applied core genome MLST (cgMLST) on isolates from a recent outbreak of AFB in Sweden. The high resolution of the cgMLST allowed different bacterial clones involved in the disease outbreak to be identified and to trace the source of infection. The source was found to be a beekeeper who had sold bees to two other beekeepers, proving the epidemiological link between them. No such conclusion could have been made using conventional MLST or ERIC-typing. This is the first time that WGS has been used to study the epidemiology of AFB. The results show that the technique is very powerful for high-resolution tracing of AFB-outbreaks.

Highlights

Paenibacillus larvae is a Gram-positive, spore-forming bacterium that causes American foulbrood disease (AFB) in honeybee larvae [1,2]
Since the owner of the infected apiary (Beekeeper 1) had other apiaries scattered throughout the island and had sold bee material to other beekeepers, an additional 42 apiaries that were either owned by or contained bees sold by the affected beekeeper were investigated for the presence of P. larvae, using culture-based microbiological assays on extracts of adult bee samples [19,24]
This study presents the use of whole-genome sequencing (WGS) and core genome multi-locus sequence typing (MLST) for separating P. larvae isolates with high resolution and the application of these techniques to trace the progress of two separate American foulbrood epidemics in Sweden

Summary

Introduction

Paenibacillus larvae is a Gram-positive, spore-forming bacterium that causes American foulbrood disease (AFB) in honeybee larvae [1,2]. It can be fatal to colonies and can be spread between apiaries unless proper control measures are carried out. AFB is highly contagious and the spread depends largely on apiculture; transportation and trading of bee material, hive equipment and honey both locally and globally [3]. In Sweden and many other countries, AFB is a notifiable disease and control measures like burning infected colonies and hive material or shaking the bees onto new wax foundations is required. The disease is widely distributed across the world causing great economic losses in apiculture [4] and is widespread in most parts of southern and central Sweden; in northern Sweden it occurs only locally.

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