Department of Applied Physics, University of Extremadura, Avda. Elvas s/n, 06071 Badajoz, Spain.
Appl Environ Microbiol. 2011 May;77(9):3102-14. doi: 10.1128/AEM.01262-10. Epub 2011 Mar 11.
High-resolution imaging of bacterial capsules by microscopy is of paramount importance in microbiology due to their role in pathogenesis. This is, however, quite a challenging task due to their delicate nature. In this context, recent reports have claimed successful exploitation of the capacity of atomic force microscopy (AFM) for imaging of extremely deformable (even liquid) surfaces under ambient conditions to detect bacterial capsules in the form of tiny amounts of liquid-like substances around bacteria. In order to further explore this supposed capacity of AFM, in this work, three staphylococcal strains have been scrutinized for the presence of capsules using such an AFM-based approach with a phosphate buffer and water as the suspending liquids. Similar results were obtained with the three strains. AFM showed the presence of liquid-like substances identical to those attributed to bacterial capsules in the previous literature. Extensive imaging and chemical analysis point out the central role of the suspending liquid (buffer) in the formation of these substances. The phenomenon has been reproduced even by using nonliving particles, a finding that refutes the biological origin of the liquid-like substances visualized around the cells. Deliquescence of major components of biological buffers, such as K(2)HPO(4), CaCl(2), or HEPES, is proposed as the fundamental mechanism of the formation of these ultrasmall liquid-like structures. Such an origin could explain the high similarity of our results obtained with three very different strains and also the high similarity of these results to others reported in the literature based on other bacteria and suspending liquids. Finally, possible biological/biomedical implications of the presence of these ultrasmall amounts of liquids wrapping microorganisms are discussed.
利用显微镜对细菌荚膜进行高分辨率成像在微生物学中至关重要，因为它们在发病机制中起作用。然而，由于其脆弱的性质，这是一项极具挑战性的任务。在这种情况下，最近的报道声称成功利用原子力显微镜（AFM）的能力在环境条件下对极可变形（甚至是液体）表面进行成像，以检测细菌荚膜，其形式是围绕细菌的少量类似液体的物质。为了进一步探索 AFM 的这种假定能力，在这项工作中，使用基于 AFM 的方法，以磷酸盐缓冲液和水作为悬浮液，检查了三种葡萄球菌菌株是否存在荚膜。三种菌株均获得了相似的结果。AFM 显示出存在与以前文献中归因于细菌荚膜的类似液体物质。广泛的成像和化学分析指出，悬浮液（缓冲液）在这些物质的形成中起着核心作用。即使使用非生命颗粒也可以重现该现象，这一发现驳斥了围绕细胞可视化的类似液体物质的生物起源。提议将生物缓冲剂的主要成分（例如 K(2)HPO(4)、CaCl(2)或 HEPES）的潮解作为这些超小类似液体结构形成的基本机制。这种起源可以解释我们用三种非常不同的菌株获得的结果高度相似，以及与其他文献中基于其他细菌和悬浮液报告的结果高度相似的原因。最后，讨论了这些包裹微生物的极少量液体存在的可能生物学/生物医学意义。
