Probiotic bacterial strains such as Escherichia coli Nissle are potentially useful for the targeted delivery of therapeutic molecules to disease sites. However, current strategies for ensuring that these Gram-negative strains deliver their cargo are mostly limited to programmed lysis or display on the outer surface of the bacteria. To promote the release of therapeutic proteins from E. coli Nissle without the requirement for lysis, Lynch et al. co-opted a type III secretion apparatus (T3SA) from Shigella flexneri that was engineered to release its payload into the bacterial surroundings rather than injecting it directly into host cells. This platform, called PROT₃EcT (probiotic type 3 secretion E. coli therapeutic), omits the tip complex from the Shigella T3SA. The tip complex would normally hold the secretion machinery in the ‘off’ configuration; in its absence, these bacterial cells secrete their cargo into the extracellular milieu without first invading host cells.

大肠杆菌Nissle等益生菌菌株可用于将治疗分子靶向递送至疾病部位。然而，目前确保这些革兰氏阴性菌株运送货物的策略主要限于程序裂解或展示在细菌的外表面。为了在不需要裂解的情况下促进大肠杆菌Nissle释放治疗性蛋白质，Lynch 等人。从志贺氏菌中增选了一种 III 型分泌装置 (T3SA)，该装置被设计为将其有效载荷释放到细菌环境中，而不是直接将其注射到宿主细胞中。这个平台，称为 PROT ₃ EcT（益生菌 3 型分泌物大肠杆菌治疗），省略了志贺氏菌T3SA的尖端复合物。尖端复合体通常会将分泌机制保持在“关闭”状态；在它不存在的情况下，这些细菌细胞将它们的货物分泌到细胞外环境中，而无需首先侵入宿主细胞。