Fate of antibiotic resistance genes and bacterial diversity during black soldier fly larvae bioconversion of human faecal waste

Human faecal waste can harbour antibiotic residues, creating reservoirs that sustain and spread antimicrobial resistance (AMR). Black soldier fly larvae (BSFL, Hermetia illucens) bioconversion has emerged as a promising strategy for processing organic waste, particularly in settings with inefficient or absent faecal waste management. However, its effects on AMR in human faecal waste remain poorly characterised. In this study, we investigated ARG dynamics and bacterial community composition during BSFL bioconversion of human faecal waste using real-time qPCR and 16S rRNA gene amplicon sequencing. Fresh faecal waste contained multiple clinically relevant ARGs conferring resistance to tetracyclines, beta-lactams, sulfonamides, fluoroquinolones, and trimethoprim. BSFL bioconversion produced time- and ARG-dependent changes, with sustained reductions in blaTEM, dfrA1, and tetA, whereas tetW and qnrB showed late enrichment. These changes occurred alongside substantial restructuring of bacterial communities, with frass developing a composition distinct from untreated faecal waste. Overall, BSFL bioconversion substantially reshaped the resistome and bacterial community but did not uniformly reduce ARGs, highlighting the potential of BSFL bioconversion as a sanitation-linked strategy to mitigate the environmental spread of AMR within a circular bioeconomy, while underscoring the need to assess residual ARGs and biosafety before downstream use of frass or larval biomass as biofertiliser or larvae as animal feed.