Establishment of apiary-level risk of American foulbrood through the detection of Paenibacillus larvae spores in pooled, extracted honey in Saskatchewan

Abstract

Paenibacillus larvae, the causative agent of American foulbrood (AFB), produces spores that may be detectable within honey. We analyzed the spore content of pooled, extracted honey from 52 large-scale (L) and 64 small-scale (S) Saskatchewan beekeepers over a two-year period (2019–2020). Our objectives were: (i) establish reliable prognostic reference ranges for spore concentrations in extracted honey to determine future AFB risk at the apiary level; (ii) identify management practices as targets for mitigation of risk. P. larvae spores were detected in 753 of 1476 samples (51%). Beekeepers were stratified into low (< 2 spores/gram), moderate (2- < 100 spores/gram), and high (≥ 100 spores/gram) risk categories. Of forty-nine L beekeepers sampled in 2019, those that reported AFB in 2020 included 0/26 low, 3/18 moderate, and 3/5 high risk. Of twenty-seven L beekeepers sampled in 2020, those that reported AFB in 2021 included 0/11 low, 2/14 moderate, and 1/2 high risk. Predictive modelling included indoor overwintering of hives, purchase of used equipment, movement of honey-producing colonies between apiaries, beekeeper demographic, and antimicrobial use as risk category predictors. Saskatchewan beekeepers with fewer than 2 spores/gram in extracted honey that avoid high risk activities may be considered at low risk of AFB the following year.

Oxytetracycline-resistant Paenibacillus larvae identified in commercial beekeeping operations in Saskatchewan using pooled honey sampling

“…29 One limitation of our study is that the pooled honey samples used for P. larvae isolation and surveillance were sampled randomly and therefore may not fully characterize the P. larvae population circulating within SK. 47,48 Investigation of the LMC susceptibility of our P. larvae isolates was hindered by lack of MIC breakpoint values for P. larvae. All P. larvae isolates tested for LMC susceptibility by the Kirby-Bauer disk diffusion assay had a zone-of-inhibition diameter less than the CLSI-defined 40-mm breakpoint for susceptibility to 4-µg LMC disks (median: 28, IQR: [26][27][28][29][30][31][32].…”

“…Accordingly, to guide antibiotic treatment decisions for AFB management, our research team developed an AFB surveillance tool that established prognostic thresholds for apiary-level risk of AFB based on P. larvae spore load in pooled, extracted honey. 47,48 Similarly, we hypothesized that pooled, extracted honey may be useful to determine the prevalence of phenotypic and genotypic determinants of antimicrobial resistance (AMR) in P. larvae, including plasmid-mediated tet(L) and tet(K) genes, known to encode membrane-associated tetracycline efflux pumps in P. larvae. 4,25,36 Moreover, genomic analysis of P. larvae isolates in honey will support molecular epidemiologic investigation of P. larvae spread, with the aid of established enterobacterial repetitive intergenic consensus (ERIC) genotyping 7,23 and multilocus sequence typing (MLST) schemes 35 for P. larvae.…”

“…Accordingly, to guide antibiotic treatment decisions for AFB management, our research team developed an AFB surveillance tool that established prognostic thresholds for apiary-level risk of AFB based on P. larvae spore load in pooled, extracted honey. 47 , 48 …”

“…The prevalence of AMR within P. larvae in our local beekeeping industry in SK, Canada is unknown, although P. larvae spores have been detected in >50% of SK honey samples. 47 , 48 Thus, to complement our previous AFB surveillance and risk assessment, and support judicious and evidence-based antimicrobial use in the beekeeping industry, our objectives were to 1) perform antimicrobial susceptibility testing of SK isolates of P. larvae cultured from pooled, extracted honey, and 2) evaluate, through whole-genome sequence (WGS) analysis, genetic determinants of AMR and phylogenetic relatedness of a subset of P. larvae isolates, representative of the range of AMR phenotypes determined in objective 1.…”

Current honey bee stressor investigations and mitigation methods in the United States and Canada

“…However, we have made relatively less progress in discerning how nonchemical disease, pest, and pathogen control techniques can effectively be used or paired with chemical control techniques to form sustainable best management practices that will be embraced by beekeepers. This work has begun for Varroa ( Berry et al 2023 , Aurell et al 2024 , Plamondon et al 2024 ), but continues to be needed for other pests and diseases such as EFB ( Grant et al 2021 ), American foulbrood ( Zabrodski et al 2022 ), chalkbrood ( Aronstein and Murray 2010 ), small hive beetles ( Mustafa et al 2014 ), Vairimorpha (formerly Nosema ) spp. ( Goblirsch 2018 ), viruses ( Beaurepaire et al 2020 ), and emerging parasites of concern such as Lotmaria passim ( Gomez-Moracho et al 2020 ) and Tropilaelaps spp.…”