Kraupner Nadine, Ebmeyer Stefan, Hutinel Marion, Fick Jerker, Flach Carl-Fredrik, Larsson D G Joakim
Centre for Antibiotic Resistance Research (CARe) at the University of Gothenburg, Gothenburg, Sweden; Department of Infectious Diseases, Institute of Biomedicine, The Sahlgrenska Academy at the University of Gothenburg, Gothenburg, Sweden.
Department of Chemistry, Umeå University, Sweden.
Environ Int. 2020 Nov;144:106083. doi: 10.1016/j.envint.2020.106083. Epub 2020 Sep 2.
Antibiotic resistance presents a serious and still growing threat to human health. Environmental exposure levels required to select for resistance are unknown for most antibiotics. Here, we evaluated different experimental approaches and ways to interpret effect measures, in order to identify what concentration of trimethoprim that are likely to select for resistance in aquatic environments. When grown in complex biofilms, selection for resistant E. coli increased at 100 µg/L, whereas there was only a non-significant trend with regards to changes in taxonomic composition within the tested range (0-100 µg/L). Planktonic co-culturing of 149 different E. coli strains isolated from sewage again confirmed selection at 100 µg/L. Finally, pairwise competition experiments were performed with engineered E. coli strains carrying different trimethoprim resistance genes (dfr) and their sensitive counterparts. While strains with introduced resistance genes grew slower than the sensitive ones at 0 and 10 µg/L, a significant reduction in cost was found already at 10 µg/L. Defining lowest effect concentrations by comparing proportion of resistant strains to sensitive ones at the same time point, rather than to their initial ratios, will reflect the advantage a resistance factor can bring, while ignoring exposure-independent fitness costs. As costs are likely to be highly dependent on the specific environmental and genetic contexts, the former approach might be more suitable as a basis for defining exposure limits with the intention to prevent selection for resistance. Based on the present and other studies, we propose that 1 µg/L would be a reasonably protective exposure limit for trimethoprim in aquatic environments.
抗生素耐药性对人类健康构成了严重且仍在不断加剧的威胁。大多数抗生素产生耐药性所需的环境暴露水平尚不清楚。在此，我们评估了不同的实验方法和解释效应指标的方式，以确定在水生环境中可能导致耐药性产生的甲氧苄啶浓度。当在复杂生物膜中生长时，对耐药大肠杆菌的选择在100微克/升时增加，而在测试范围内（0 - 100微克/升），分类组成的变化仅呈现出不显著的趋势。对从污水中分离出的149种不同大肠杆菌菌株进行浮游共培养，再次证实了在100微克/升时会出现选择现象。最后，对携带不同甲氧苄啶耐药基因（dfr）的工程化大肠杆菌菌株及其敏感对应菌株进行了成对竞争实验。虽然在0和10微克/升时，导入耐药基因的菌株生长速度比敏感菌株慢，但在10微克/升时就已发现耐药性成本显著降低。通过比较同一时间点耐药菌株与敏感菌株的比例，而非与它们的初始比例，来定义最低效应浓度，将反映出耐药因素所能带来的优势，同时忽略与暴露无关的适应性成本。由于成本可能高度依赖于特定的环境和遗传背景，前一种方法可能更适合作为定义暴露限值的基础，以防止产生耐药性。基于本研究及其他研究，我们建议1微克/升可作为水生环境中甲氧苄啶合理的保护性暴露限值。
