Two novel ISCR1-associated dfr genes, dfrA42 and dfrA43, were identified from trimethoprim (TMP)-resistant Proteus strains and were shown to confer high levels of TMP resistance (MIC, ≥1,024 mg/liter) when cloned into Escherichia coli isolates. These genes were hosted by complex class 1 integrons, suggesting their potential for dissemination. Analyses of enzymatic parameters and TMP affinity were performed, and the results suggested that the mechanism of TMP resistance for these novel dihydrofolate reductases (DHFRs) is the reduction of binding with TMP.

中文翻译：

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两个新的 ISCR1 相关基因 dfrA42 和 dfrA43 的鉴定和表征，编码甲氧苄氨嘧啶抗性二氢叶酸还原酶

两个新的 IS CR1相关dfr基因dfrA42和dfrA43从耐甲氧苄氨嘧啶 (TMP) 的变形杆菌菌株中鉴定出来，并显示当克隆到大肠杆菌分离株中时赋予高水平的 TMP 抗性（MIC，≥1,024 毫克/升）。这些基因由复杂的 1 类整合子托管，表明它们具有传播潜力。对酶参数和 TMP 亲和力进行了分析，结果表明这些新型二氢叶酸还原酶 (DHFR) 的 TMP 抗性机制是与 TMP 结合的减少。