Endolysin CHAP domain-carbosilane metallodendrimer complexes with triple action on Gram-negative bacteria: Membrane destabilization, reactive oxygen species production and peptidoglycan degradation

Bacterial resistance to antibiotics is a significant challenge that is associated with increased morbidity and mortality. Gram-negative bacteria are particularly problematic due to an outer membrane (OM). Current alternatives to antibiotics include antimicrobial peptides or proteins and multifunctional systems such as dendrimers. Antimicrobial proteins such as lysins can degrade the bacterial cell wall, whereas dendrimers can permeabilize the OM, enhancing the activity of endolysins against gram-negative bacteria. In this study, we present a three-stage action of endolysin combined with two different carbosilane (CBS) silver metallodendrimers, in which the periphery is modified with N-heterocyclic carbene (NHC) ligands coordinating a silver atom. The different NHC ligands contained hydrophobic methyl or N-donor pyridyl moieties. The effects of these endolysin/dendrimer combinations are based on OM permeabilization, peptidoglycan degradation, and reactive oxygen species production. The results showed that CBS possess a permeabilization effect (first action), significantly reduced bacterial growth at higher concentrations alone and in the presence of endolysin, increased ROS production (second action), and led to bacterial cell damage (third action). The complex formed between the CHAP domain of endolysin and a CBS silver metallodendrimer, with a triple mechanism of action, may represent an excellent alternative to other antimicrobials with only one resistance mechanism.

抗菌药物耐药性是导致发病率和死亡率增加的重大挑战，其中革兰氏阴性细菌因其外膜（OM）的存在而尤为棘手。当前抗生素的替代品包括抗菌肽或蛋白质以及如树枝状聚合物等多功能系统。如溶菌酶等抗菌蛋白能够降解细菌细胞壁，而树枝状聚合物则能够使外膜通透化，从而增强内溶菌酶对革兰氏阴性细菌的活性。在本研究中，我们提出了一种内溶菌酶与两种不同的碳硅烷（CBS）银金属树枝状聚合物相结合的三阶段作用机制，其中外围经过N-杂环卡宾（NHC）配体的修饰，并与银原子配位。不同的NHC配体包含疏水的甲基或N-供体吡啶基团。这些内溶菌酶/树枝状聚合物组合的作用基于外膜通透化、肽聚糖降解和活性氧的产生。结果显示，CBS具有通透化效应（第一阶段），在较高浓度下单独使用或在存在内溶菌酶的情况下显著减少细菌生长，增加活性氧的产生（第二阶段），并导致细菌细胞损伤（第三阶段）。内溶菌酶的CHAP结构与CBS银金属树枝状聚合物形成的复合物，具有三重作用机制，可能成为其他仅具有单一耐药机制抗菌药物的理想替代品。