Biogeography of Paenibacillus larvae, the causative agent of American foulbrood, using a new multilocus sequence typing scheme.

Barbara J Morrissey,Giles E Budge,Thorunn Helgason,Anne Fünfhaus,Lena Poppinga,Elke Genersch

doi:10.1111/1462-2920.12625

Abstract

American foulbrood is the most destructive brood disease of honeybees (Apis mellifera) globally. The absence of a repeatable, universal typing scheme for the causative bacterium Paenibacillus larvae has restricted our understanding of disease epidemiology. We have created the first multilocus sequence typing scheme (MLST) for P. larvae, which largely confirms the previous enterobacterial repetitive intergenic consensus (ERIC)–polymerase chain reaction (PCR)-based typing scheme's divisions while providing added resolution and improved repeatability. We have used the new scheme to determine the distribution and biogeography of 294 samples of P. larvae from across six continents. We found that of the two most epidemiologically important ERIC types, ERIC I was more diverse than ERIC II. Analysis of the fixation index (FST) by distance suggested a significant relationship between genetic and geographic distance, suggesting that population structure exists in populations of P. larvae. Interestingly, this effect was only observed within the native range of the host and was absent in areas where international trade has moved honeybees and their disease. Correspondence analysis demonstrated similar sequence type (ST) distributions between native and non-native countries and that ERIC I and II STs mainly have differing distributions. The new typing scheme facilitates epidemiological study of this costly disease of a key pollinator.

Highlights

Paenibacillus larvae, a Gram-positive spore-forming bacterium, causes American foulbrood (AFB), which is the most destructive brood disease of the honeybee (Apis mellifera)
Paenibacillus larvae spores are able to remain infective for more than 35 years in old hives and are resistant to extremes of temperature (Hasemann, 1961). This makes the control of the disease difficult because human activity can spread the disease over long distances and previously dormant strains may cause an outbreak several years after the original outbreak
AFB is a serious disease of honeybee brood with near global distribution; disease epidemiology is poorly understood, in part due to an absence of a repeatable method to discriminate between strain types

Summary

Introduction

Paenibacillus larvae, a Gram-positive spore-forming bacterium, causes American foulbrood (AFB), which is the most destructive brood disease of the honeybee (Apis mellifera). The spores are infective and are fed to bee brood by nurse bees in contaminated larval food (glandular secretions and processed honey) (Yue et al, 2008). Paenibacillus larvae spores are able to remain infective for more than 35 years in old hives and are resistant to extremes of temperature (Hasemann, 1961). This makes the control of the disease difficult because human activity can spread the disease over long distances and previously dormant strains may cause an outbreak several years after the original outbreak

Results

Discussion

Conclusion