A metagenomic survey reveals widespread antibiotic resistance genes in honey bee ( Apis mellifera ) gut bacteria across the United States

ABSTRACT Antibiotic use has contributed to antibiotic resistance genes (ARGs) accumulating in many environments, including host-associated microbiomes. Managed honey bee gut bacteria may accumulate ARGs, as honey bees are sometimes treated with antibiotics and often live in agricultural landscapes contaminated with antibiotics. We describe the occurrence and distribution of ARGs in honey bee bacterial gut symbionts from 13 apiaries in a transect across the USA from Washington to Virginia. Using metagenomic sequencing, we detected 55 unique ARGs conferring resistance to 14 classes of antibiotics. Of these, 11 ARGs encoded multidrug resistance. ARGs varied among sites, and ARG composition in hives shifted across the transect. Among honey bee gut bacterial genera, ARG occurrence varied, with Gilliamella and Frischella containing the highest proportions of ARGs despite their low relative abundance in the gut community, suggesting specific genera may serve as ARG reservoirs. As tetracycline is the most used antibiotic in beekeeping, we compared the frequency and abundance of tetracycline resistance genes across apiaries. All hives contained tetracycline resistance genes, with tetB and tetM present at all apiaries. Based on qPCR, tetB and tetM abundance varied significantly among apiaries. TetB was higher overall and declined in abundance from Washington to Virginia. We demonstrate that honey bee gut bacteria possess a diversity of ARGs, not all of which are consistent with antibiotic use in beekeeping, ARG frequency varies among bacterial genera in the honey bee gut, and certain ARGs are associated with hive geographic location. IMPORTANCE The spread of antibiotic resistance genes (ARGs) to bacterial pathogens is a critical issue facing global health. Gut bacterial symbionts of managed honey bees make good bioindicators for ARGs because honey bees interact with potential environmental reservoirs of ARGs and are broadly distributed across the USA, including in both urban and rural environments. Based on our transect across the USA, ARGs were diverse and widely distributed among honey bee gut symbionts, although certain bacterial genera had a higher propensity for accumulating ARGs. Tetracycline resistance genes were most common, and varied in occurrence and abundance across the transect. The abundance of tetB , in particular, increased from east to west along the sampled transect. These large-scale patterns of ARG distribution within a widely dispersed host-associated microbiome system provide a foundation from which to examine the underlying factors driving differences in ARG occurrence and abundance.