Profiling of extracellular antibiotic resistance genes during antibiotic production wastewater treatment processes: Occurrence, transformation dynamics, and potential hosts

The propagation of antibiotic resistance genes (ARGs) in both intracellular and extracellular forms during wastewater treatment processes has garnered increasing attention. Antibiotic production wastewater (APW) contains high concentrations of antibiotics and organics known to induce the transformation of extracellular ARGs (eARGs) and potentially facilitate antibiotic resistance transmission. In this study, the presence, transformation dynamics, and potential hosts of eARGs in a full-scale APW treatment plant (APWTP) were investigated. Free-eARGs (f-eARGs) were prevalent in the effluent (5.0 ×10⁶ copies/mL), comprising 54.9 % of total ARGs. APW significantly increased the transforming ability of eARGs compared to municipal wastewater, with this effect being significantly greater than that of the antibiotics at influent concentration levels. This promotion effect was likely due to increased oxidative stress and bacterial membrane permeability, and reduced concomitantly with the removal of conventional wastewater pollutants (e.g., COD and NH₃-N); however, such effect persisted after treatment. Based on cell sorting and high-throughput sequencing, several opportunistic pathogens, such as Pseudomonas, Stenotrophomonas, and Acinetobacter, demonstrated a heightened propensity to uptake eARGs, posing a greater threat to human health. These findings underscore the significant contributions of eARGs to the spread of antibiotic resistance in WTPs, particularly when treating APW.