h Manure from swine treated with antimicrobials as feed additives is a major source for the expansion of the antibiotic resistance gene (ARG) reservoir in the environment. Vermicomposting via housefly larvae (Musca domestica) can be efficiently used to treat manure and regenerate biofertilizer, but few studies have investigated its effect on ARG attenuation. Here, we tracked the abundances of 9 ARGs and the composition and structure of the bacterial communities in manure samples across 6 days of fullscale manure vermicomposting. On day 6, the abundances of genes encoding tetracycline resistance [tet(M), tet(O), tet(Q), and tet(W)] were reduced (P < 0.05), while those of genes encoding sulfonamide resistance (sul1 and sul2) were increased (P < 0.05) when normalized to 16S rRNA. The abundances of tetracycline resistance genes were correlated (P < 0.05) with the changing concentrations of tetracyclines in the manure. The overall diversity and richness of the bacteria significantly decreased during vermicomposting, accompanied by a 100 times increase in the relative abundance of Flavobacteriaceae spp. Variations in the abundances of ARGs were correlated with the changing microbial community structure and the relative abundances of the family Ruminococcaceae, class Bacilli, or phylum Proteobacteria. Vermicomposting, as a waste management practice, can reduce the overall abundance of ARGs. More research is warranted to assess the use of this waste management practice as a measure to attenuate the dissemination of antimicrobial residues and ARGs from livestock production before vermicompost can be safely used as biofertilizer in agroecosystems.A ntimicrobials have been widely used at therapeutic levels for microbial infection control and at subtherapeutic levels for growth promotion as veterinary feed additives, administered in water or parenterally in animal husbandry (1). Antimicrobials can select for antibiotic resistance genes (ARGs) in host-associated bacteria from concentrated animal feeding operations and in the environment where antimicrobial-containing feces are excreted or applied to fields (2). Through horizontal gene transfer mechanisms triggered by mobile genetic elements, such as conjugative plasmids, integrons, and transposons (3, 4), different microbes can share their genetic information, potentially causing the transfer and dissemination of ARGs from feces-associated bacteria to indigenous environmental microbes. For instance, an intI1 gene encoding a site-specific integrase responsible for integration is closely related to the transfer of sulfonamide resistance genes among bacteria (5). Specifically, swine manure increases the resistant gene reservoir in the environment, as most applied veterinary antimicrobials are poorly absorbed by livestock (6). These antimicrobials are largely excreted in feces and then dispersed to soil when the manure is used as fertilizer. Unmanaged waste disposal is commonly regarded as one of the major sources for the environmental expansion of ARGs (3); therefore, it is ext...