Antibiotic acyldepsipeptides (ADEPs) exert potent antibacterial activity in rodent models of bacterial infection and exceptional efficacy against persister cells of methicillin-resistant Staphylococcus aureus (MRSA). The mechanism of ADEP action is unusual in that the antibiotic releases the destructive capacity of over-activated ClpP, the proteolytic core of the bacterial Clp protease. The essential bacterial cell division protein FtsZ had emerged in a previous study as a preferred protein substrate of ADEP-activated ClpP but it is definitely not the only cellular substrate.

In the current study, we set out to follow the morphological changes that lead to ADEP-mediated bacterial death in S. aureus and Bacillus subtilis, differentiating between antibacterial effects at low and high ADEP concentrations. Here, fluorescence and time-lapse microscopy data show that cells adopt a characteristic phenotype of cell division inhibition at ADEP levels close to the MIC, but retain the capacity to form viable daughter cells for a substantial period of time when transferred to ADEP-free growth medium. After extended exposure to low ADEP concentrations, nucleoids of B. subtilis started to disorganize and upon compound removal many cells failed to re-organize nucleoids, re-initiate cytokinesis and consequently died. Survival versus cell death of filamentous cells attempting recovery depended on the timing of completion of new septa in relation to the loss of cell envelope integrity. We show that the potential to recover after ADEP removal depends on the antibiotic concentration as well as the treatment duration. When exposed to ADEP at concentrations well above the MIC, biomass production ceased rapidly as did the potential to recover. In time-kill studies both long-time exposure to low ADEP levels as well as short-time exposure to high concentrations proved highly effective, while intermittent concentrations and time frames were not. We here provide new insights into the antimicrobial activity of ADEP antibiotics and the consequences of dosing and timing for bacterial physiology which should be considered in view of a potential therapeutic application of ADEPs.

抗生素酰基肽肽（ADEPs）在啮齿动物细菌感染模型中发挥有效的抗菌活性，并且对耐甲氧西林的金黄色葡萄球菌（MRSA）的持久性细胞具有卓越的功效。ADEP作用的机制是不同寻常的，因为抗生素释放了过度活化的ClpP（细菌Clp蛋白酶的蛋白水解核心）的破坏能力。在先前的研究中，必需的细菌细胞分裂蛋白FtsZ已经成为ADEP激活的ClpP的优选蛋白底物，但它绝对不是唯一的细胞底物。

在当前的研究中，我们着手跟踪导致金黄色葡萄球菌和枯草芽孢杆菌ADEP介导的细菌死亡的形态变化，以区分低和高ADEP浓度下的抗菌作用。在这里，荧光和延时显微镜数据显示，细胞在接近MIC的ADEP水平上具有细胞分裂抑制的特征表型，但是当转移至无ADEP的生长过程中，在相当长的一段时间内仍保留了形成存活子代细胞的能力。中等的。在长期暴露于低ADEP浓度后，枯草芽孢杆菌的核苷开始分解，并且在去除化合物后，许多细胞无法重组核苷，重新启动胞质分裂并因此死亡。生存与试图恢复的丝状细胞的细胞死亡取决于与细胞包膜完整性丧失有关的新隔膜完成的时间。我们表明，ADEP去除后恢复的潜力取决于抗生素浓度以及治疗持续时间。当暴露于浓度远高于MIC的ADEP时，生物质生产迅速停止，潜在的恢复能力也迅速停止。在时间杀灭研究中，长期暴露于低ADEP水平以及短期暴露于高浓度都被证明是非常有效的，而间歇性浓度和时限却没有。我们在这里提供有关ADEP抗生素的抗菌活性以及细菌生理剂量和给药时间的后果的新见解，鉴于ADEP的潜在治疗应用，应考虑这些后果。