Rapidly mitigating antibiotic resistant risks in chicken manure by Hermetia illucens bioconversion with intestinal microflora

Authors: CAI, MINMIN - Huazhong Agricultural University; MA, SHITENG - Huazhong Agricultural University; HU, RUIQI - Huazhong Agricultural University; TOMBERLIN, JEFFREY - Texas A&M University; Thomashow, Linda; ZHENG, LONGYU - Huazhong Agricultural University; LI, WU - Huazhong Agricultural University; YU, ZINIU - Huazhong Agricultural University; ZHANG, JIBIN - Huazhong Agricultural University

Submitted to: Environmental Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/11/2018
Publication Date: 10/11/2018
Citation: Cai, M., Ma, S., Hu, R., Tomberlin, J.K., Thomashow, L.S., Zheng, L., Li, W., Yu, Z., Zhang, J. 2018. Rapidly mitigating antibiotic resistant risks in chicken manure by Hermetia illucens bioconversion with intestinal microflora. Environmental Microbiology. 20(11):4051-4062. https://doi.org/10.1111/1462-2920.14450.
DOI: https://doi.org/10.1111/1462-2920.14450

Interpretive Summary: Antibiotic resistance genes (ARGs) in animal manure contribute to the increase in multidrug-resistant pathogens in the environment and are a hazard to public health. The treatment of animal manure with fly larvae is a promising alternative to traditional and developing manure processing strategies to reduce the abundance of ARG in the environment. In this study, we treated chicken manure by traditional methods used on the farm, or with the larvae (an immature worm-like form) of black soldier fly, a large, harmless fly maintained in the laboratory. We designed three treatment systems including sterile and non-sterile larvae and traditional compost treatments to study the dynamics of target ARGs, bacterial community structure, and changing environmental factors as the fly larvae consumed and processed the manure in their guts. We found that treatment with the larvae reduced the risks associated with the spread of ARGs by up to 95% during chicken manure treatment. ARG genes and genes involved in their transfer among bacteria in the environment were much reduced, and human pathogenic bacterial populations also decreased significantly in manure treated for 12 days with the larvae. Non-sterile larval treatments had lower and more stable ARG distributions and might be more effective than sterile treatments. We conclude that these advantages can be attributed to the activity of larvae with their intestinal bacteria and likely are due to selective pressures imposed by microbial exposure to the alternating manure and larval gut environments as the bacteria pass through the larvae, to the antibacterial activity of the larvae themselves, and to the reduced nutrients available to bacteria carrying antibiotic resistance genes as the larvae consume the manure.

Technical Abstract: Antibiotic resistance genes (ARGs) in animal manure contribute to the increase in multidrug-resistant pathogens in the environment and are a hazard to public health. The bioconversion of manure with fly larvae is a promising alternative to traditional and developing manure processing strategies to reduce the abundance of ARGs. Here, we investigated the ability of black soldier fly (BSF, Hermetia illucens) larvae to suppress the persistence of ARGs in chicken manure bioconversion and suggest three mechanisms by which ARGs are eliminated. Compared to traditional compost, compost treated with BSF larvae was reduced by an average of 95% in absolute abundance of ARG and integrin genes due at least in part to rapid decreases in concentrations of the genes and of bacteria in the larval gut. Bacterial community composition also differed significantly in treated as compared to untreated manure, with the percentage of Firmicutes that can carry ARGs reduced by at least 65.5%. On average, populations of bacterial genera pathogenic to humans declined by 70.7-92.9%, effectively mitigating the risk of these bacteria carrying ARGs. Environmental pH, nitrogen content and tetracycline antibiotic concentrations were closely related to both bacterial community composition and target gene attenuation in the larval treatment system. We suggest that selective pressures imposed by microbial exposure to the alternating manure and larval gut environments, larval bacteriostasis, and reformulation of the manure environment due to consumption by BSF larvae contribute to ARG attenuation.