Department of Chemistry and Biochemistry, The University of Texas at Austin, Austin, Texas, USA.
mBio. 2010 Oct 12;1(4):e00202-10. doi: 10.1128/mBio.00202-10.
Bacteria are social organisms that display distinct behaviors/phenotypes when present in groups. These behaviors include the abilities to construct antibiotic-resistant sessile biofilm communities and to communicate with small signaling molecules (quorum sensing [QS]). Our understanding of biofilms and QS arises primarily from in vitro studies of bacterial communities containing large numbers of cells, often greater than 10(8) bacteria; however, in nature, bacteria often reside in dense clusters (aggregates) consisting of significantly fewer cells. Indeed, bacterial clusters containing 10(1) to 10(5) cells are important for transmission of many bacterial pathogens. Here, we describe a versatile strategy for conducting mechanistic studies to interrogate the molecular processes controlling antibiotic resistance and QS-mediated virulence factor production in high-density bacterial clusters. This strategy involves enclosing a single bacterium within three-dimensional picoliter-scale microcavities (referred to as bacterial "lobster traps") defined by walls that are permeable to nutrients, waste products, and other bioactive small molecules. Within these traps, bacteria divide normally into extremely dense (10(12) cells/ml) clonal populations with final population sizes similar to that observed in naturally occurring bacterial clusters. Using these traps, we provide strong evidence that within low-cell-number/high-density bacterial clusters, QS is modulated not only by bacterial density but also by population size and flow rate of the surrounding medium. We also demonstrate that antibiotic resistance develops as cell density increases, with as few as ~150 confined bacteria exhibiting an antibiotic-resistant phenotype similar to biofilm bacteria. Together, these findings provide key insights into clinically relevant phenotypes in low-cell-number/high-density bacterial populations.
细菌是具有社会行为的生物体，当它们聚集在一起时，会表现出明显的行为/表型。这些行为包括构建抗生素耐药性的固着生物膜群落的能力，以及用小的信号分子（群体感应 [QS]）进行通信的能力。我们对生物膜和 QS 的理解主要来自于含有大量细胞的细菌群落的体外研究，通常大于 10(8)个细菌；然而，在自然界中，细菌通常存在于由显著较少的细胞组成的密集聚集体（聚集物）中。事实上，含有 10(1) 到 10(5)个细胞的细菌聚集体对于许多细菌病原体的传播很重要。在这里，我们描述了一种灵活的策略，用于进行机制研究，以探究控制高密度细菌聚集体中抗生素耐药性和 QS 介导的毒力因子产生的分子过程。该策略涉及将单个细菌包裹在三维皮升级微腔（称为细菌“龙虾陷阱”）内，这些微腔由允许营养物质、废物和其他生物活性小分子通过的壁定义。在这些陷阱内，细菌正常分裂成非常密集的（10(12)个细胞/ml）克隆群体，最终群体大小与自然发生的细菌聚集体中观察到的相似。使用这些陷阱，我们提供了强有力的证据表明，在低细胞数/高密度细菌聚集体中，QS 不仅受到细菌密度的调节，还受到周围介质的种群大小和流速的调节。我们还证明，随着细胞密度的增加，抗生素耐药性会发展，即使只有~150 个被限制的细菌也表现出类似于生物膜细菌的抗生素耐药表型。这些发现共同为低细胞数/高密度细菌群体中的临床相关表型提供了重要的见解。
