Although nano-self-assemblies of hydrophobic-modified bacitracin A with poly(d,l-lactic-co-glycolic acid) (PLGA) (nano-BA_PLGA) have demonstrated promising antibacterial activities, the application of nano-BA_PLGA was severely compromised by low water solubility. In this study, a series of PEGylated PLGA copolymers were selected to conjugate with the N-terminus of bacitracin A to construct PEGylated self-assembled nano-BAs and to further develop nano-self-assemblies of bacitracin A with strong antibacterial potency and high solubility. Compared with nano-BA_PLGA, all PEGylated nano-BAs, except nano-BA_5k, exhibited strong antibacterial efficiency against both Gram-positive and Gram-negative bacteria by inducing loss of cytoplasmic membrane potential, membrane permeabilization, and leakage of calcein from artificial cell membranes. Studies elucidating the underlying mechanism of PEGylated nano-BAs against Gram-negative bacteria indicated that the strong hydrophobic and van der Waals interactions between PLGA and lipopolysaccharide (LPS) could bind, neutralize, and disassociate LPS, facilitating cellular uptake of the nanoparticles, which could destabilize the membrane, resulting in cell death. Moreover, PEGylated nano-BAs (nano-BA_12k) with a longer PLGA block were expected to occupy a higher local density of BA mass on the surface and result in stronger hydrophobic and van der Waals interactions with LPS, which were responsible for the enhanced antibacterial activity against Gram-positive and emerging antibacterial activity against Gram-negative bacteria, respectively. In vivo imaging verified that PEGylated nano-BAs exhibited higher inflammatory tissue distribution and longer circulation time than nano-BA_PLGA. Therefore, although PEGylation did not affect antibacterial activity, it is necessary for target delivery and resistance to clearance of the observed PEGylated nano-BAs. In vivo, nano-BA_12k also showed the highest therapeutic index against infection burden in a mouse thigh infection model among the tested formulations, which showed good correlation with the in vitro results. In conclusion, nano-BA_12k showed high efficacy in the treatment of invasive infections. This new approach of constructing nanoantibiotics by modification of commercially available antibiotics with PEGylated copolymers is safe, cost-effective, and environmentally friendly.

中文翻译：

---

聚乙二醇化的自组装纳米杆菌肽A：探讨体内靶标递送的抗菌机制和实时追踪

尽管疏水修饰的杆菌肽A与聚（d，l-乳酸-共-乙醇酸）（PLGA）（nano-BA _PLGA）的纳米自组装已显示出令人鼓舞的抗菌活性，但nano-BA _PLGA的应用非常严格低水溶性会损害其性能。在这项研究中，选择一系列的聚乙二醇化PLGA共聚物与杆菌肽A的N端缀合，以构建聚乙二醇化的自组装纳米BA，并进一步开发具有强大抗菌力和高溶解度的杆菌肽A的纳米自组装体。 。与nano-BA _PLGA相比，除nano-BA _5k外，所有聚乙二醇化nano-BA通过诱导细胞质膜电位的丧失，膜的透化作用以及钙黄绿素从人工细胞膜的泄漏，对革兰氏阳性和革兰氏阴性细菌均表现出强大的抗菌作用。研究阐明了聚乙二醇化纳米BAs对革兰氏阴性细菌的潜在机制，表明PLGA与脂多糖（LPS）之间的强疏水性和范德华相互作用可以结合，中和并解离LPS，从而促进细胞对纳米颗粒的摄取，从而可以破坏膜的稳定性，导致细胞死亡。此外，聚乙二醇化的纳米BA（nano-BA _12k）具有更长PLGA嵌段的化合物预计会在表面上占据较高的BA物质局部密度，并导致与LPS的更强的疏水性和范德华相互作用，从而增强了对革兰氏阳性细菌的抗菌活性，并逐渐增强了对BPS的抗菌活性革兰氏阴性菌。体内成像证实，与纳米BA _PLGA相比，聚乙二醇化的纳米BA具有更高的炎症组织分布和更长的循环时间。因此，尽管聚乙二醇化不影响抗菌活性，但是对于靶标递送和观察到的聚乙二醇化纳米BA的清除抵抗仍是必需的。体内，nano-BA _12k在所测试的制剂中，Richards还显示出在小鼠大腿感染模型中针对感染负担的最高治疗指数，这与体外结果显示出良好的相关性。总之，nano-BA _12k在治疗侵袭性感染方面显示出很高的疗效。通过使用聚乙二醇化共聚物修饰市售抗生素来构建纳米抗生素的新方法是安全，经济高效且环境友好的。