Li Kun, Li Ting, Yang Shan-Shan, Wang Xu-De, Gao Lei-Xin, Wang Rui-Qi, Gu Jing, Zhang Xian-En, Deng Jiao-Yu
Key Laboratory of Agricultural and Environmental Microbiology, Wuhan Institute of Virology, Chinese Academy of Sciences, Wuhan, China.
National Laboratory of Biomacromolecules, Institute of Biophysics, Chinese Academy of Sciences, Beijing, China
Antimicrob Agents Chemother. 2017 Apr 24;61(5). doi: 10.1128/AAC.02378-16. Print 2017 May.
Co-trimoxazole, a fixed-dose combination of sulfamethoxazole (SMX) and trimethoprim (TMP), has been used for the treatment of bacterial infections since the 1960s. Since it has long been assumed that the synergistic effects between SMX and TMP are the consequence of targeting 2 different enzymes of bacterial folate biosynthesis, 2 genes ( and ) involved in the folate biosynthesis of were deleted, and their effects on the susceptibility to antifolates were tested. The results showed that the deletion of resulted in a lag of growth in minimal medium and increased susceptibility to both SMX and TMP. Moreover, deletion of also greatly enhanced the bactericidal effect of TMP. To elucidate the mechanism of how the deletion of affects the bacterial growth and susceptibility to antifolates, 7,8-dihydroneopterin and 7,8-dihydropteroate were supplemented into the growth medium. Although those metabolites could restore bacterial growth, they had no effect on susceptibilities to the antifolates. Reverse mutants of the deletion strain were isolated to further study the mechanism of how the deletion of affects susceptibility to antifolates. Targeted sequencing and subsequent genetic studies revealed that the disruption of the tetrahydromonapterin biosynthesis pathway could reverse the phenotype caused by the deletion. Meanwhile, overexpression of could also lead to increased susceptibility to both SMX and TMP. These data suggested that the deletion of resulted in the excess production of tetrahydromonapterin, which then caused the increased susceptibility to antifolates. In addition, we found that the deletion of also resulted in increased susceptibility to both SMX and TMP in Since dihydroneopterin triphosphate hydrolase is an important component of bacterial folate biosynthesis and the tetrahydromonapterin biosynthesis pathway also exists in a variety of bacteria, it will be interesting to design new compounds targeting dihydroneopterin triphosphate hydrolase, which may inhibit bacterial growth and simultaneously potentiate the antimicrobial activities of antifolates targeting other components of folate biosynthesis.
复方新诺明是磺胺甲恶唑（SMX）和甲氧苄啶（TMP）的固定剂量组合，自20世纪60年代以来一直用于治疗细菌感染。由于长期以来人们一直认为SMX和TMP之间的协同作用是靶向细菌叶酸生物合成的两种不同酶的结果，因此删除了参与细菌叶酸生物合成的两个基因（和），并测试了它们对抗叶酸药物敏感性的影响。结果表明，的缺失导致在基本培养基中生长滞后，并增加了对SMX和TMP的敏感性。此外，的缺失也大大增强了TMP的杀菌效果。为了阐明缺失如何影响细菌生长和对抗叶酸药物的敏感性的机制，在生长培养基中添加了7,8-二氢新蝶呤和7,8-二氢蝶酸。尽管这些代谢产物可以恢复细菌生长，但它们对抗叶酸药物的敏感性没有影响。分离出缺失菌株的回复突变体，以进一步研究缺失如何影响对抗叶酸药物敏感性的机制。靶向测序和随后的遗传学研究表明，四氢单蝶呤生物合成途径的破坏可以逆转缺失引起的表型。同时，的过表达也会导致对SMX和TMP的敏感性增加。这些数据表明，的缺失导致四氢单蝶呤的过量产生，进而导致对抗叶酸药物的敏感性增加。此外，我们发现的缺失也导致细菌对SMX和TMP的敏感性增加。由于二氢新蝶呤三磷酸水解酶是细菌叶酸生物合成的重要组成部分，并且四氢单蝶呤生物合成途径也存在于多种细菌中，因此设计靶向二氢新蝶呤三磷酸水解酶的新化合物可能会抑制细菌生长，并同时增强针对叶酸生物合成其他成分的抗叶酸药物的抗菌活性，这将是很有趣的。
