Data from: CRISPR-based herd immunity limits phage epidemics in bacterial populations

Herd immunity, a process in which resistant individuals limit the spread of a pathogen among susceptible hosts has been extensively studied in eukaryotes. Even though bacteria have evolved multiple immune systems against their phage pathogens, herd immunity in bacteria remains unexplored. Here we experimentally demonstrate that herd immunity arises during phage epidemics in structured and unstructured Escherichia coli populations consisting of differing frequencies of susceptible and resistant cells harboring CRISPR immunity. In addition, we develop a mathematical model that quantifies how herd immunity is affected by spatial population structure, bacterial growth rate, and phage replication rate. Using our model we infer a general epidemiological rule describing the relative speed of an epidemic in partially resistant spatially structured populations. Our experimental and theoretical findings indicate that herd immunity may be important in bacterial communities, allowing for stable coexistence of bacteria and their phages and the maintenance of polymorphism in bacterial immunity.群体免疫（herd immunity）是指抗性个体可限制病原体在易感宿主间传播的过程，该过程已在真核生物中得到广泛研究。尽管细菌已演化出多种抵御噬菌体病原体的免疫系统，但细菌群体免疫仍未得到探索。本研究通过实验证实，在携带CRISPR免疫的易感与抗性细胞比例各异的结构化与非结构化大肠杆菌种群中，噬菌体流行期间会出现群体免疫现象。此外，本研究构建了一个数学模型，可量化空间种群结构、细菌生长速率以及噬菌体复制速率对群体免疫的影响。基于该模型，本研究推导得到一条通用流行病学规律，可描述部分抗性空间结构化种群中流行病的相对传播速度。本研究的实验与理论结果表明，群体免疫在细菌群落中或发挥重要作用，可实现细菌与其噬菌体的稳定共存，并维持细菌免疫的多态性。