Abstract：
As emerging contaminants, antibiotics are frequently present in various environments, particularly rivers, albeit often at sublethal concentrations (ng/L∼μg/L). Assessing the risk associated with these low levels, which are far below the lethal threshold for most organisms, remains challenging. In this study, using microcosms containing planktonic bacteria and biofilm, we examined how antibiotic resistance genes (ARGs) in different physical states, including intracellular ARGs (iARGs) and extracellular ARGs (eARGs) responded to these low-level antibiotics. Our findings reveal a positive correlation between sub-lethal antibiotic exposure (ranging from 0.1 to 10 μg/L) and increased prevalence (measured as ARG copies/16s rDNA) of both iARGs and eARGs in planktonic bacteria. Notably, eARGs demonstrated greater sensitivity to antibiotic exposure compared to iARGs, with a lower threshold (0.1 μg/L for eARGs versus 1 μg/L for iARGs) for abundance increase. Moreover, ARGs in biofilms demonstrates higher sensitivity to antibiotic exposure compared to planktonic bacteria. To elucidate the underlying mechanisms, we established an integrated population dynamics-pharmacokinetics-pharmacodynamics (PD-PP) model. This model indicates that the enhanced sensitivity of eARGs is primarily driven by an increased potential for plasmid release from cells under low antibiotic concentrations. Furthermore, the accumulation of antibiotic in biofilms induces a greater sensitivity of ARG compared to the planktonic bacteria. This study provides a fresh perspective on the development of antibiotic resistance and offers an innovative approach for assessing the risk of sublethal antibiotic in the environment.
摘要：
作为新兴的污染物，抗生素经常出现在各种环境中，尤其是河流,尽管通常处于亚致死浓度（ng/L~μg/L）。评估与这些低水平相关的风险，远低于大多数生物的致命阈值，仍然具有挑战性。在这项研究中,利用含有浮游细菌和生物膜的微观世界，我们研究了抗生素抗性基因(ARGs)在不同的物理状态下，包括细胞内ARGs（iARGs）和细胞外ARGs（eARGs）对这些低水平抗生素有反应。我们的发现表明，亚致死抗生素暴露（0.1至10μg/L）与浮游细菌中iARG和eARG的患病率增加（以ARG拷贝/16srDNA衡量）之间呈正相关。值得注意的是,与iARGs相比，eARGs对抗生素暴露的敏感性更高，丰度增加的阈值较低(eARGs为0.1μg/L，iARGs为1μg/L)。此外，与浮游细菌相比，生物膜中的ARG对抗生素暴露具有更高的敏感性。为了阐明潜在的机制，我们建立了一个综合的群体动力学-药代动力学-药效学(PD-PP)模型.该模型表明，eARG的敏感性增强主要是由在低抗生素浓度下从细胞释放质粒的可能性增加驱动的。此外，与浮游细菌相比，抗生素在生物膜中的积累诱导了更高的ARG敏感性。这项研究为抗生素耐药性的发展提供了新的视角，并提供了一种评估环境中亚致死抗生素风险的创新方法。
