Sludge management optimization for mitigating the antimicrobial resistance dissemination
Abstract
Antimicrobial resistance (AMR) is a major concern with respect to global public health. The persistence and dissemination of AMR concern encompasses human, animal and environment issues and thus fits into the One Health framework. AMR has been quantified in multiple compartments of aquatic and terrestrial ecosystems and wastewater treatment plants were pointed out as a major source of AMR dissemination into the environment, including through sludge spreading as a soil fertilization practice. In this study, the dynamics of antibiotics and antimicrobial resistance were investigated along the sludge – sludge treatment process – soil continuum. For this purpose, 5 sludge treatments were carried out in the laboratory on the same raw sludge : drying, liming, composting, anaerobic digestion, and anaerobic digestion followed by composting. Soil microcosms were then conducted for mimicking the spreading of the raw and 5 treated sludges in agricultural soil. To better constrain the driving processes, sludge samples were placed into litterbags, between two soil layers. Antibiotics were quantified all along the sludge treatments and during the soil incubation. Antimicrobial resistance was captured using culture-dependent as well as culture-independent methodologies (e.g. high-throughput quantitative PCR) for characterizing the total microbial communities, the abundance and diversity of the resistant bacteria and genes, but also the mobile genetic elements. The most abundant AMR genes in raw sludge were those encoding for resistance to aminoglycosides (aadA and strB), sulfonamides (sul1), macrolides (ermB) and transposases. The higher the overall biological activity (in intensity and diversity), the higher the AMR removal. This was true during sludge treatment as well as during soil incubation. The main outputs of this work are thus the hierarchisation of the sludge treatment according to their ability to mitigate the antimicrobial resistance dissemination, but also the identification of the main factors triggering antibiotic resistance dissemination.