Effects of antibacterial agents and drugs monitored by atomic force microscopy

Abstract

Originally invented for topographic imaging, atomic force microscopy (AFM) has evolved into a multifunctional biological toolkit, enabling to measure structural and functional details of cells and molecules. Its versatility and the large scope of information it can yield make it an invaluable tool in any biologically oriented laboratory, where researchers need to perform characterizations of living samples as well as single molecules in quasi-physiological conditions and with nanoscale resolution. In the last 20 years, AFM has revolutionized the characterization of microbial cells by allowing a better understanding of their cell wall and of the mechanism of action of drugs and by becoming itself a powerful diagnostic tool to study bacteria. Indeed, AFM is much more than a high-resolution microscopy technique. It can reconstruct force maps that can be used to explore the nanomechanical properties of microorganisms and probe at the same time the morphological and mechanical modifications induced by external stimuli. Furthermore it can be used to map chemical species or specific receptors with nanometric resolution directly on the membranes of living organisms. In summary, AFM offers new capabilities and a more in-depth insight in the structure and mechanics of biological specimens with an unrivaled spatial and force resolution. Its application to the study of bacteria is extremely significant since it has already delivered important information on the metabolism of these small microorganisms and, through new and exciting technical developments, will shed more light on the real-time interaction of antimicrobial agents and bacteria.

Atomic Force Microscopy in Microbiology: New Structural and Functional Insights into the Microbial Cell Surface

“…In summary, nanomechanical experiments have enabled new light to be shed into how cell surface sensors, adhesins, and pili respond to mechanical stimuli in relation to function. Note that besides protein mechanics, cell mechanics can also be addressed by AFM force spectroscopy, enabling us for instance to assess the impact of antibiotics on cell stiffness (83, 84). …”

Real-Time Monitoring of Protein Conformational Changes Using a Nano-Mechanical Sensor

“…Among them, Atomic Force Microscope (AFM) microcantilever sensors are now routinely used to study ligand-receptor interactions [21], [22]. Due to their sensitivity and their large dynamical range, cantilever sensors have the potential to provide a breakthrough in the investigation and characterization of biological systems [23] including conformational changes in proteins [24] and, in particular, the ATP hydrolysis in enzymes [25]. However, up to now, such capabilities have not been exploited to investigate in detail the dynamics of these conformational changes, restricting the focus on static effects [26], [27].…”

Nanomechanical motion of Escherichia coli adhered to a surface

“…14,15 In static and resonant sensing modalities, microcantilevers have allowed for the sensing of diverse biological entities, ranging from DNA to proteins to microorganisms [16][17][18] (e.g., viruses and bacteria). In more recent work, Longo et al 19,20 adhered bacteria to a microcantilever, and measured the nanomechanical fluctuations of the cantilever before and after bacteria adhesion. With the bacteria present on the cantilever, the fluctuations increased significantly.…”

“…In this letter, we apply the microcantilever-based technique developed by Longo et al 19,20 to measurements of the nature (e.g., time scales and amplitudes) of the forces that bacteria exert on the microcantilever. We start with time domain measurements, in which we observe an increase in the variance of the microcantilever fluctuations due to bacterial motion.…”