PDF(Pubmed)
Abstract：
Clostridioides difficile is the leading cause of antibiotic-associated diarrhea worldwide with significant morbidity and mortality. This organism is naturally resistant to several beta-lactam antibiotics that inhibit the polymerization of peptidoglycan, an essential component of the bacteria cell envelope. Previous work has revealed that C. difficile peptidoglycan has an unusual composition. It mostly contains 3-3 cross-links, catalyzed by enzymes called L,D-transpeptidases (Ldts) that are poorly inhibited by beta-lactams. It was therefore hypothesized that peptidoglycan polymerization by these enzymes could underpin antibiotic resistance. Here, we investigated the catalytic activity of the three canonical Ldts encoded by C. difficile (LdtCd1, LdtCd2, and LdtCd3) in vitro and explored their contribution to growth and antibiotic resistance. We show that two of these enzymes catalyze the formation of novel types of peptidoglycan cross-links using meso-diaminopimelic acid both as a donor and an acceptor, also observed in peptidoglycan sacculi. We demonstrate that the simultaneous deletion of these three genes only has a minor impact on both peptidoglycan structure and resistance to beta-lactams. This unexpected result therefore implies that the formation of 3-3 peptidoglycan cross-links in C. difficile is catalyzed by as yet unidentified noncanonical Ldt enzymes.
摘要：
艰难梭菌是世界范围内抗生素相关性腹泻的主要原因,具有显著的发病率和死亡率。这种生物对抑制肽聚糖聚合的几种β-内酰胺抗生素具有天然抗性，细菌细胞包膜的重要组成部分。先前的工作已经揭示艰难梭菌肽聚糖具有不寻常的组成。它主要包含3-3个交联，由叫做L的酶催化，β-内酰胺类对D-转肽酶(Ldts)的抑制作用较差。因此,假设通过这些酶的肽聚糖聚合可以支持抗生素抗性。这里,我们在体外研究了由艰难梭菌编码的三种规范Ldts（LdtCd1，LdtCd2和LdtCd3）的催化活性，并探讨了它们对生长和抗生素抗性的贡献。我们表明，这些酶中的两种使用内消旋二氨基庚二酸（DAP）作为供体和受体来催化新型肽聚糖交联的形成，在肽聚糖囊中也观察到。我们证明了这三个基因的同时缺失仅对肽聚糖结构和对β-内酰胺的抗性具有较小的影响。因此,该出乎意料的结果暗示艰难梭菌中3-3个肽聚糖交联的形成是由尚未鉴定的非规范Ldt酶催化的。
