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American foulbrood (AFB) is an infectious disease of honey bee brood caused by the endospore-forming bacterium Paenibacillus larvae. P. larvae spores are resilient in the environment, thus colonies with clinical signs of AFB are often destroyed by burning to eradicate the causative agent. To prevent outbreaks of AFB, oxytetracycline metaphylaxis is widely used in North America, resulting in sustained selective pressure for oxytetracycline resistance in P. larvae. To determine if antimicrobial resistance (AMR) is present among P. larvae isolates from commercial beekeeping operations in Saskatchewan, Canada, we performed antimicrobial susceptibility testing of 718 P. larvae samples cultured from pooled, extracted honey collected from 52 beekeepers over a 2-y period, 2019 and 2020. We found that 65 of 718 (9%) P. larvae samples collected from 8 beekeepers were resistant to oxytetracycline with minimum inhibitory concentration (MIC) values of 64–256 µg/mL. Eight of 718 (1%) samples from 4 beekeepers had intermediate resistance to oxytetracycline (MIC: 4–8 µg/mL). Susceptibility testing for tylosin and lincomycin indicated that P. larvae in Saskatchewan continue to be susceptible to these antimicrobials (tylosin MIC: <1 µg/mL, lincomycin MIC: ≤2 µg/mL). Most oxytetracycline-resistant P. larvae samples were identified in northeastern Saskatchewan. Whole-genome sequence analysis identified the P. larvae –specific plasmid pMA67 with tetracycline-resistance gene tet (L) in 9 of 11 oxytetracycline-resistant P. larvae isolates sequenced. Our results highlight the advantage of using pooled, extracted honey as a surveillance tool for monitoring AMR in P. larvae. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Three commercial honey bee operations in Saskatchewan, Canada, with outbreaks of American foulbrood (AFB) and recent or ongoing metaphylactic antibiotic use were intensively sampled to detect spores of Paenibacillus larvae during the summer of 2019. Here, we compared spore concentrations in different sample types within individual hives, assessed the surrogacy potential of honey collected from honey supers in place of brood chamber honey or adult bees within hives, and evaluated the ability of pooled, extracted honey to predict the degree of spore contamination identified through individual hive testing. Samples of honey and bees from hives within apiaries with a recent, confirmed case of AFB in a single hive (index apiaries) and apiaries without clinical evidence of AFB (unaffected apiaries), as well as pooled, apiary-level honey samples from end-of-season extraction, were collected and cultured to detect and enumerate spores. Only a few hives were heavily contaminated by spores in any given apiary. All operations were different from one another with regard to both the overall degree of spore contamination across apiaries and the distribution of spores between index apiaries and unaffected apiaries. Within operations, individual hive spore concentrations in unaffected apiaries were significantly different from index apiaries in the brood chamber (BC) honey, honey super (HS) honey, and BC bees of one of three operations. Across all operations, BC honey was best for discriminating index apiaries from unaffected apiaries (p = 0.001), followed by HS honey (p = 0.06), and BC bees (p = 0.398). HS honey positively correlated with both BC honey (rs = 0.76, p < 0.0001) and bees (rs = 0.50, p < 0.0001) and may be useful as a surrogate for either. Spore concentrations in pooled, extracted honey seem to have predictive potential for overall spore contamination within each operation and may have prognostic value in assessing the risk of future AFB outbreaks at the apiary (or operation) level. [ABSTRACT FROM AUTHOR]