Characteristics of tylosin and enrofloxacin degradation in swine manure digested by black soldier fly (Hermetia illucens L.) larvae

Abstract

Black soldier fly, Hermetia illucens L. (Diptera: Stratiomyidae) larvae (BSF larvae or BSFL) offer an environmental-friendly method for degrading antibiotics, such as tylosin (TYL) and enrofloxacin (EF), in swine manure. This study examined the impact of temperature on this process, role of associated microbes, dynamics of resistant genes, and a description of the microbial community associated with the BSF larval gut, how microbes isolated from the BSF larval gut as inoculants impact the process as well as enhance antibiotic digestion, and finally a quantification of antibiotics in BSF larvae fed manure with TYL or EF. Antibiotic degradation in manure was optimized at 28 °C with at least 10% greater than 23 °C and 37 °C. More than 40% reduction in TYL and EF concentrations in the manure occurred when BSF larval gut associated microbes were present. Furthermore, DNA extracted from the gut of non-sterile BSF larvae fed manure with TYL or EF indicated at least two 2-△△Ct fold increase in antibiotic resistance genes for TYL and EF. We identified 250, 4, and 16 unique operational taxa for larvae fed control manure and manure with either TYL or EF. Intestinal microbes isolated from non-sterile larvae fed manure with TYL or EF, were identified, cultured, and examined for their ability to degrade TYL and EF in Luria-Bertani (LB) medium. Three strains (two strains of Enterococcus faecalis and one strain of Proteus mirabilis) resulted in at least 50% TYL or EF degradation within 96 h. Sterile BSF larvae inoculated with P. mirabilis recovered >60% of the degradation ability exhibited by non-sterile larvae. Finally, no TYL residuals were found in 14-d-old larvae, prepupae, or pupae of BSF immatures fed manure containing these antibiotics. While ∼65 μg/g and ∼20 μg/g of EF were found in larval contents and pupal exoskeleton, respectively.