Department of Mechanical & Materials Engineering, University of Nebraska-Lincoln, Lincoln, Nebraska, USA.
Department of Pathology & Microbiology, University of Nebraska Medical Center, Omaha, Nebraska, USA.
mSphere. 2019 Jul 17;4(4):e00372-19. doi: 10.1128/mSphere.00372-19.
bacteria form biofilms and distinctive microcolony or "tower" structures that facilitate their ability to tolerate antibiotic treatment and to spread within the human body. The formation of microcolonies, which break off, get carried downstream, and serve to initiate biofilms in other parts of the body, is of particular interest here. It is known that flow conditions play a role in the development, dispersion, and propagation of biofilms in general. The influence of flow on microcolony formation and, ultimately, what factors lead to microcolony development are, however, not well understood. The hypothesis being examined is that microcolony structures form within a specific range of levels of shear stress. In this study, laminar shear flow over a range of 0.15 to 1.5 dynes/cm was examined. It was found that microcolony structures form in a narrow range of shear stresses around 0.6 dynes/cm Further, measurements of cell density as a function of space and time showed that shear dependence can be observed hours before microcolonies form. This is significant because, among other physiologic flows, this is the same shear stress found in large veins in the human vasculature, which, along with catheters of similar diameters and flow rates, may therefore play a critical role in biofilm development and subsequent spreading of infections throughout the body. It is well known that flow plays an important role in the formation, transportation, and dispersion of biofilms. What was heretofore not known was that the formation of tower structures in these biofilms is strongly shear stress dependent; there is, in fact, a narrow range of shear stresses in which the phenomenon occurs. This work quantifies the observed shear dependence in terms of cell growth, distribution, and fluid mechanics. It represents an important first step in opening up a line of questioning as to the interaction of fluid forces and their influence on the dynamics of tower formation, break-off, and transportation in biofilms by identifying the parameter space in which this phenomenon occurs. We have also introduced state-of-the-art flow measurement techniques to address this problem.
细菌形成生物膜和独特的微菌落或“塔”结构，这有助于它们耐受抗生素治疗并在人体内传播。这里特别关注的是微菌落的形成，微菌落会脱落，被携带到下游，并在身体的其他部位引发生物膜。众所周知，流动条件在生物膜的发展、分散和传播中起着作用。然而，流动对微菌落形成的影响以及哪些因素最终导致微菌落的发展还不是很清楚。正在检验的假设是，微菌落结构在特定的剪切应力范围内形成。在这项研究中，考察了 0.15 到 1.5 达因/平方厘米范围内的层流剪切。结果发现，微菌落结构在 0.6 达因/平方厘米左右的狭窄剪切应力范围内形成。此外，细胞密度随空间和时间的测量表明，在微菌落形成前几个小时就可以观察到剪切依赖性。这是重要的，因为在其他生理流动中，这与人体血管中的大静脉中的剪切应力相同，而与类似直径和流速的导管一起，可能在生物膜的发展和随后的感染在整个身体中的传播中起着关键作用。众所周知，流动在生物膜的形成、运输和分散中起着重要作用。以前不知道的是，这些生物膜中塔结构的形成强烈依赖于剪切应力；实际上，在发生这种现象的狭窄剪切应力范围内。这项工作根据细胞生长、分布和流体力学来量化观察到的剪切依赖性。它代表了一个重要的第一步，即通过确定发生这种现象的参数空间，开辟了一条关于流体力的相互作用及其对生物膜中塔形成、断裂和运输动力学影响的问题的研究路线。我们还引入了先进的流动测量技术来解决这个问题。
