Microbial Ecology of European Foul Brood Disease in the Honey Bee (Apis mellifera): Towards a Microbiome Understanding of Disease Susceptibility

Abstract

European honey bees (Apis mellifera Linnaeus) are beneficial insects that provide essential pollination services for agriculture and ecosystems worldwide. Modern commercial beekeeping is plagued by a variety of pathogenic and environmental stressors often confounding attempts to understand colony loss. European foulbrood (EFB) is considered a larval-specific disease whose causative agent, Melissococcus plutonius, has received limited attention due to methodological challenges in the field and laboratory. Here, we improve the experimental and informational context of larval disease with the end goal of developing an EFB management strategy. We sequenced the bacterial microbiota associated with larval disease transmission, isolated a variety of M.plutonius strains, determined their virulence against larvae in vitro, and explored the potential for probiotic treatment of EFB disease. The larval microbiota was a low diversity environment similar to honey, while worker mouthparts and stored pollen contained significantly greater bacterial diversity. Virulence of M. plutonius against larvae varied markedly by strain and inoculant concentration. Our chosen probiotic, Parasaccharibacter apium strain C6, did not improve larval survival when introduced alone, or in combination with a virulent EFB strain. We discuss the importance of positive and negative controls for in vitro studies of the larval microbiome and disease.

Overwintering Honey Bee Colonies: Effect of Worker Age and Climate on the Hindgut Microbiota

“…Additionally, for one of their major experiments, Kešnerová et al (2019) [ 36 ] pooled 20 guts for each phenotype, whereas we examined individuals. Several recent studies indicate that when dysbiotic, the individual gut microbiome can increase substantially in size [ 34 , 35 ], such that a single dysbiotic individual could dominate the sampling results among 20 healthy individuals. Lastly, the microbiomes detailed by Kešnerová (2019) [ 36 ] may represent a recurrent enterotype because the non-winter seasons are dominated by Gilliamella with lesser amounts of Lactobacillus firm5 [ 27 ].…”

“…Lastly, the microbiomes detailed by Kešnerová (2019) [ 36 ] may represent a recurrent enterotype because the non-winter seasons are dominated by Gilliamella with lesser amounts of Lactobacillus firm5 [ 27 ]. Most nurse/forager honeybee hindgut microbiomes sampled from non-winter are dominated by Lactobacillus firm5 [ 20 , 21 , 22 , 23 , 26 , 27 , 28 , 29 , 30 , 31 , 32 , 33 , 34 , 35 ]. Although both hindgut enterotypes are potentially healthy, they may react differently to perturbation or seasonal changes.…”

“…Core hind gut bacteria Lactobacillus Firm5, Lactobacillus Firm4 and Bifidobacterium asteroides are associated with the rectum while Lactobacillus Firm5, Snodgrassella alvi , Gilliamella apicola and Frischella perrara are associated with the ileum/pylorus [ 28 , 29 ]. Found less frequently and in lower abundance in the worker hindgut are Bartonella apis , Bombella apis [ 30 , 31 ] and Lactobacillus kunkeei , the latter two being more commonly associated with the hive environment, mouthparts, larvae and queens [ 20 , 21 , 22 , 23 , 26 , 27 , 28 , 29 , 30 , 31 , 32 , 33 , 34 , 35 ]. Although the gut microbiota of workers, queens and larvae have been studied, the gut microbiota of the diutinus phenotype has been largely overlooked.…”

Antimicrobial Resistance Genes in Bacteria Isolated From Japanese Honey, and Their Potential for Conferring Macrolide and Lincosamide Resistance in the American Foulbrood Pathogen Paenibacillus larvae

“…In the recent 16S rRNA gene amplicon sequencing for investigating microbiota in honey, Lactobacillus kunkeei ( Apilactobacillus kunkeei ), Parasacharribacter apium ( Bombella apis ), Fructobacillus fructosus , Gilliamella apicola , Xanthomonadales and Actinomycetales were detected as major bacterial species/groups at the DNA level ( Floyd et al, 2020 ). Other previous studies reported that aerobic spore-forming bacteria of the genera Paenibacillus and Bacillus are commonly found in honey ( Snowdon and Cliver, 1996 ; Alippi et al, 2004 ; López and Alippi, 2007 ; López et al, 2008 ).…”

“…OTC-resistant phenotypes observed in P. larvae develop, at least in part, due to plasmids carrying the tetracycline resistance gene [ tet (L)], and the plasmids may be transferable across bacterial species ( Murray and Aronstein, 2006 ; Alippi et al, 2007 , 2014 ; Murray et al, 2007 ). In honey, many bacteria, including Bacillus and Paenibacillus species, are known to exist ( Snowdon and Cliver, 1996 ; Alippi et al, 2004 ; Sinacori et al, 2014 ; Floyd et al, 2020 ). In a previous study, López et al (2008) isolated Bacillus cereus strains carrying a variety of tetracycline and OTC resistance genes, including tet (L) and tet (K), from honey, and suggested that bacteria in honey are a reservoir for tetracycline resistance genes.…”