Navigating through soft and highly confined environments is crucial for bacteria moving within living organisms’ tissues, yet this topic has been less explored. In our study, we experimentally harnessed the unique biconcave geometry of red blood cells (RBCs) to enable real-time visualization of swimming Escherichia coli interacting with soft RBCs. Our findings show that RBCs adhering to a rigid surface can enclose spaces comparable to the size of bacteria, effectively entrapping them. Remarkably, we found that bacteria can escape from this extremely confined space through three newly defined escape modes: Bundling, Unbundling, and Flipping, each mode relying on the specific states of bacterial flagella. A quantitative analysis uncovers significant differences among these modes in terms of scattering angle, escaping speed, and trapping duration. We used two methods to alter the rigidity and adhesion strength of RBCs, and we studied their effects on the detailed bacterial escape process. Our results contribute to the knowledge of bacterial migration in soft, confined spaces, thereby enhancing our understanding of similar processes in biological tissue environments.

中文翻译：

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细菌从柔软的密闭空间逸出的游泳模式


在柔软和高度狭窄的环境中导航对于细菌在生物体组织内移动至关重要，但这个话题的探索较少。在我们的研究中，我们实验性地利用了红细胞 （RBC） 独特的双凹几何形状，实现了游泳的大肠杆菌与软 RBC 相互作用的实时可视化。我们的研究结果表明，粘附在刚性表面的红细胞可以封闭与细菌大小相当的空间，有效地捕获它们。值得注意的是，我们发现细菌可以通过三种新定义的逃逸模式从这个极其狭窄的空间逃逸：Bbundleling、Unbundling 和 Flipping，每种模式都依赖于细菌鞭毛的特定状态。定量分析揭示了这些模式在散射角度、逃逸速度和捕获持续时间方面的显著差异。我们使用了两种方法来改变红细胞的刚度和粘附强度，并研究了它们对详细细菌逃逸过程的影响。我们的结果有助于了解细菌在柔软、狭窄空间中的迁移，从而增强我们对生物组织环境中类似过程的理解。