Increasing microbial resistance, coupled with a lack of new antimicrobial discovery, has led researchers to refocus on antimicrobial peptides (AMPs) as novel therapeutic candidates. Significantly, the less toxic cecropins have gained widespread attention for potential antibacterial agent development. However, the narrow activity spectrum and long sequence remain the primary limitations of this approach. In this study, we truncated and modified cecropin 4 (41 amino acids) by varying the charge and hydrophobicity balance to obtain smaller AMPs. The derivative peptide C18 (16 amino acids) demonstrated high antibacterial activity against Gram-negative and Gram-positive bacteria, as well as yeasts. Moreover, C18 demonstrated a minimal inhibitory concentration (MIC) of 4 µg/mL against the methicillin-resistant Staphylococcus aureus (MRSA) and showed synergy with daptomycin with a fractional inhibition concentration index (FICI) value of 0.313. Similar to traditional cecropins, C18 altered the membrane potential, increased fluidity, and caused membrane breakage at 32 µg/mL. Importantly, C18 eliminated 99% persisters at 10 × MIC within 20 min and reduced the biofilm adherence by ~40% and 35% at 32 and 16 µg/mL. Besides, C18 possessed a strong binding ability with DNA at 7.8 μM and down-regulated the expression of virulence factor genes like agrA, fnb-A, and clf-1 by more than 5-fold (p < 0.05). Interestingly, in the Galleria mellonella model, C18 rescued more than 80% of larva infected with the MRSA throughout 120-h post-infection at a single dose of 8 mg/kg (p < 0.05). In conclusion, this study provides a reference for the transformation of cecropin to derive small peptides and presents C18 as an attractive therapeutic candidate to be developed to treat severe MRSA infections.

中文翻译：

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新型天蚕素 4 衍生肽对抗耐甲氧西林金黄色葡萄球菌

微生物耐药性的增加，加上缺乏新的抗菌药物发现，导致研究人员重新关注抗菌肽（AMP）作为新的治疗候选物。值得注意的是，毒性较低的天蚕素因其潜在抗菌剂的开发而受到广泛关注。然而，窄的活性谱和长的序列仍然是这种方法的主要限制。在本研究中，我们通过改变电荷和疏水性平衡来截短和修饰天蚕素 4（41 个氨基酸）以获得更小的 AMP。衍生肽 C18（16 个氨基酸）对革兰氏阴性菌、革兰氏阳性菌以及酵母菌具有较高的抗菌活性。此外，C18 对耐甲氧西林金黄色葡萄球菌(MRSA)的最低抑制浓度 (MIC) 为 4 µg/mL ，并与达托霉素显示出协同作用，抑制浓度指数 (FICI) 值为 0.313。与传统天蚕素类似，C18 改变膜电位，增加流动性，并在 32 µg/mL 浓度时引起膜破裂。重要的是，C18 在 10 × MIC 下可在 20 分钟内消除 99% 的残留细胞，并在 32 和 16 µg/mL 下使生物膜粘附减少约 40% 和 35%。此外，C18 在 7.8 μM 下与 DNA 具有很强的结合能力，并将 agrA、fnb-A 和 clf-1 等毒力因子基因的表达下调 5 倍以上 ( p < 0.05)。有趣的是，在大蜡螟模型中，C18 在感染后 120 小时内以 8 mg/kg 单剂量拯救了超过 80% 的感染 MRSA 的幼虫（p < 0.05）。总之，本研究为天蚕素转化为小肽提供了参考，并提出 C18 作为一种有吸引力的候选药物，可用于治疗严重的 MRSA 感染。