Developing Phage Therapy That Overcomes the Evolution of Bacterial Resistance开发可克服细菌抗药性进化的噬菌体疗法

4. Minimizing Bacterial Resistance
4.尽量减少细菌抗药性

The straightforward approach to overcome bacterial resistance to phages is to design a phage therapy that maximizes the rate of phage killing across genotypes of target clinical isolates, thus restricting bacteria from growing to large population sizes. Reduced population size limits the ability for a bacterial population to overcome an environmental challenge (55), such as resistance to lytic phage attack. As spontaneous mutations occur randomly in genomes, population size must be above a certain threshold for these rescue mutations to arise and spread to fixation. Thus, minimizing the bacterial population size decreases the chance that bacteria can persist alongside lytic phages and therefore reduces the likelihood for evolved phage resistance. As an added benefit, the patient’s immune system and/or other administered antimicrobials can more easily clear the reduced population size (bacterial load) of survivors following initial phage deployment.
克服细菌对噬菌体抗药性的直接方法是设计一种噬菌体疗法，最大限度地提高噬菌体对目标临床分离株不同基因型的杀灭率，从而限制细菌增长到较大的种群规模。种群规模的缩小限制了细菌种群克服环境挑战的能力（55），例如对溶解性噬菌体攻击的抗性。由于基因组中的自发突变是随机发生的，因此种群数量必须超过一定的阈值，这些拯救性突变才会出现并扩散至固定状态。因此，尽量缩小细菌种群规模会降低细菌与噬菌体同时存在的几率，从而降低噬菌体抗性进化的可能性。此外，患者的免疫系统和/或其他抗菌药物也能更容易地清除初始噬菌体部署后数量减少（细菌负荷）的幸存者。

4.1. Choosing Highly Efficient Phages
4.1.选择高效噬菌体

Using efficiently propagating phages can contribute to reducing bacterial numbers. Some traits of the lytic phage replication cycle (56, 57) that may be desirable for maximizing therapeutic phage killing include adsorption kinetics, latent periods, and burst size. A phage that adsorbs strongly to one or more binding targets on the cell surface essentially maximizes rapid and irreversible adsorption to susceptible cells (58, 59). Latent period, the time between phage adsorption and release of new phages via cell lysis, should be minimized to achieve more rounds of infections per unit time (60). Large burst sizes are also beneficial because they result in generation of up to thousands of new offspring phage particles per cellular infection, thereby increasing the likelihood that the target bacterial population is overwhelmed by the presence of a smaller number of phages (60). Last, phage stability (e.g., avoidance of particle degradation and/or aggregation) is crucial for long-term storage of phages and may increase virus durability when administered to the patient.
使用高效繁殖的噬菌体有助于减少细菌数量。为了最大限度地发挥噬菌体的治疗杀灭作用，溶菌噬菌体复制周期 ( 56, 57) 的一些特征可能是理想的，其中包括吸附动力学、潜伏期和爆发大小。噬菌体如果能强烈吸附细胞表面的一个或多个结合目标，就能最大限度地快速、不可逆地吸附到易感细胞上 ( 58, 59)。潜伏期是指从噬菌体吸附到通过细胞裂解释放新噬菌体之间的时间，应尽量缩短潜伏期，以便在单位时间内实现更多轮感染（60）。大爆发量也有好处，因为每次细胞感染都会产生多达数千个新的子代噬菌体颗粒，从而增加目标细菌群被少量噬菌体淹没的可能性（60）。最后，噬菌体的稳定性（如避免颗粒降解和/或聚集）对噬菌体的长期储存至关重要，可提高病毒在患者体内的耐久性。

All of these phage traits can be determined in the lab using standard microbiological techniques (61–64), where the aim could be to identify individual viruses with maximal performance traits or to combine different phages together that collectively exhibit optimal traits.
所有这些噬菌体特性都可以在实验室中利用标准微生物学技术进行测定 ( 61-64) ，目的是找出具有最佳性能特性的单个病毒，或将不同的噬菌体组合在一起，共同表现出最佳特性。

Here we describe various studies that address this overarching goal to minimize the evolutionary potential of target bacteria (Figure 3), using naturally occurring phages, those experimentally evolved in the laboratory, and viruses that are genetically engineered.
在这里，我们介绍了针对这一总体目标的各种研究，这些研究利用自然产生的噬菌体、实验室中实验进化的噬菌体以及基因工程改造的病毒，最大限度地降低了目标细菌的进化潜力（图 3）。