The ecological security risks of phthalates: A focus on antibiotic resistance gene dissemination in aquatic environments

Antibiotic resistance genes (ARGs) have become a major focus in environmental safety and human health, with concerns about non-antibiotic substances like microplastics facilitating their horizontal gene transfer. Phthalate esters (PAEs), as ubiquitous plastic additives, are prevalent in aquatic environments, yet there remains a dearth of studies examining their impacts on ARG dissemination. This study focuses on dibutyl phthalate (DBP), a prototypical PAE, to assess its potential influence on the conjugative transfer of ARGs along with the related molecular mechanisms. The results revealed that DBP exposure at environmentally relevant concentrations significantly promoted the conjugative transfer of RP4 plasmid-mediated ARGs by up to 2.7-fold compared to that of the control group, whereas it severely suppressed the conjugation at a high concentration (100 μg/L). The promotion of conjugation transfer by low-concentration DBP (0.01-10 μg/L) was mainly attributed to the stimulation of ROS, enhanced membrane permeability, increased energy synthesis, increased polymeric substances secretion, and upregulation of conjugation-related genes. Conversely, high DBP exposure induced oxidative damage and reduced ATP synthesis, resulting in the suppression of ARG conjugation. Notably, donor and recipient bacteria responded differently to DBP-induced oxidative stress. This study explores the environmental behavior of DBP in the water environment from the perspective of ARG propagation and provides essential data and theoretical insights to raise public awareness about the ecological security risks of PAEs.