Synthetic biology has focused on engineering microbes to synthesize useful products or to serve as living diagnostics and therapeutics. Here we utilize a host-derived Escherichia coli strain engineered with a genetic toggle switch as a research tool to examine in vivo replicative states in a mouse model of chronic infection, and to compare in vivo and in vitro bacterial behavior. In contrast to the effect of antibiotics in vitro, we find that the fraction of actively dividing bacteria remains relatively high throughout the course of a chronic infection in vivo and increases in response to antibiotics. Moreover, the presence of non-dividing bacteria in vivo does not necessarily lead to an antibiotic-tolerant infection, in contrast to expectations from in vitro experiments. These results demonstrate the utility of engineered bacteria for querying pathogen behavior in vivo, and the importance of validating in vitro studies of antibiotic effects with in vivo models.

合成生物学的重点是工程微生物，以合成有用的产品或用作活的诊断和治疗方法。在这里，我们利用宿主来源的大肠杆菌用遗传拨动开关设计的菌株作为研究工具，用于检查慢性感染小鼠模型中的体内复制状态，并比较体内和体外细菌行为。与体外抗生素的作用相反，我们发现在整个体内慢性感染的过程中，活跃分裂细菌的比例仍然相对较高，并且对抗生素的反应有所增加。此外，与体外实验的预期相反，体内非分裂细菌的存在并不一定导致抗生素耐受性感染。这些结果证明了工程菌在体内查询病原体行为的实用性，以及利用体内模型验证抗生素作用的体外研究的重要性。