Mechanical properties of biological specimens explored by atomic force microscopy

The atomic force microscope is a widely used surface scanning apparatus capable of reconstructing at a nanometric scale resolution the 3D morphology of biological samples. Due to its unique sensitivity, it is now increasingly used as a force sensor, to characterize the mechanical properties of specimens with a similar lateral resolution. This unique capability has produced, in the last years, a vast increase in the number of groups that have exploited the versatility and sensitivity of the instrument to explore the nanomechanics of various samples in the fields of biology, microbiology and medicine. In this review we outline the state of the art in this field, reporting the most interesting recent works involving the exploration of the nanomechanical properties of various biological samples.

Effects of antibacterial agents and drugs monitored by atomic force microscopy

Sandor Kasas, Giovanni Longo

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 20years, 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. For further resources related to this article, please visit the . Conflict of interest: The authors have declared no conflicts of interest for this article.

Wiley-Blackwell2014

Adaptation of Pseudomonas aeruginosa to constant sub-inhibitory concentrations of quaternary ammonium compounds

Myriam Borgatta, Florian Frédéric Vincent Breider, Giovanni Dietler, Sandor Kasas, Leonardo Venturelli, Urs von Gunten

Quaternary ammonium compounds (QACs) are widely used in consumer products for disinfection purposes. QACs are frequently detected in aquatic systems at sub-inhibitory concentrations and were found to affect the development of antimicrobial resistance if bacteria are exposed to increasing concentrations. However, the effect of a constant sub-inhibitory concentration on the development of bacterial resistance is unknown. A constant exposure to 88% of the minimum inhibitory concentration (MIC) of benzalkonium chloride (BAC) led to an increase of the MIC of P. aeruginosa. It increased from 80 mg l-1 to 150 mg l-1 after 10 cycles of exposure and remained stable after removal of BAC. When P. aeruginosa was exposed to cetyltrimethyl ammonium chloride (CTMA), the MIC increased from 110 mg l-1 to 160 mg l-1 after 10 cycles of exposure and decreased to 120 mg l-1 after removal of CTMA. Additionally, cross-resistance between the QACs was observed. When exposed to BAC, the MIC for CTMA increased from 110 mg l-1 to 200 mg l-1, and when exposed to CTMA, the MIC for BAC increased from 80 mg l-1 to 160 mg l-1. In contrast, the susceptibility to 16 antibiotics was not significantly affected by exposure to QACs. Finally, analyses of the membranes’ nanomechanical properties of P. aeruginosa with atomic force microscopy (AFM) showed increases in cell roughness, adhesion and stiffness after treatment with CTMA. Since sub-inhibitory concentrations of QACs can be detected in aquatic systems, this may lead to a dissemination of bacteria with higher QAC resistance in the environment.

2020

Resistance to disinfection agents: Adaptation of P. aeruginosa to sub inhibitory concentrations of quaternary ammonium compounds (QACs)

Florian Frédéric Vincent Breider, Leonardo Venturelli, Urs von Gunten, Margaux Océane Voumard

Quaternary ammonium compounds (QACs) are among the most used disinfection agents in consumer products and in industrial applications. Because of their poor biodegradabil ity, after use, they will persist in technical and natural aquatic systems at sub - inhibitory concentrations. Implications of QACs on the development of antimicrobial resistance was detected in several studies, however, the effect of a constant sub - inhibito ry concentration on the development of bacterial resistance remains unknown. The aim of this study was to determine if constant sub - inhibitory concentrations of benzalkonium chloride (BAC) and cetyltrimethylammonium chloride (CTMA) are able to promote a st able adaptation of populations of P. aeruginosa . Additionally, the study investigated cross - resistances between QACs and with antibiotics and nanomechanical properties of the membrane using atomic force microscopy (AFM) were explored. The exposure to sub - i nhibitory concentrations of QACs led to a maximal but reversible increase of the minimum inhibitory concentration (MIC) by a factor 1.45 for CTMA and a maximal irreversible increase of the MIC by a factor 1.9 for BAC. Cross - resistance was observed with the QACs but not with antibiotics: bacteria exposed to CTMA had an increased MIC for BAC of a factor 1.8 and bacteria exposed to BAC had an increased MIC for CTMA of a factor 1.75. Analyses of the membrane by AFM showed increase in the cell's roughness and st iffness after treatment with QACs. In populations of P. aeruginosa, constant sub - inhibitory concentrations of QACs were able to promote adaptations mechanisms, which were irreversible in the case of BAC. Furthermore, cross - resistance between the selected Q ACs were observed. Since low sub - inhibitory concentrations of QACs can be detected in natural and technical aquatic systems, this may lead to a dissemination of bacteria with higher QAC resistance or with QAC multiresistance, which can be a threat to the u rban water management.

2019

Resistance to disinfection agents: Adaptation of P. aeruginosa to sub inhibitory concentrations of quaternary ammonium compounds (QACs)

Florian Frédéric Vincent Breider, Leonardo Venturelli, Urs von Gunten, Margaux Océane Voumard

2019

Mechanical properties of biological specimens explored by atomic force microscopy

Effects of antibacterial agents and drugs monitored by atomic force microscopy

Adaptation of Pseudomonas aeruginosa to constant sub-inhibitory concentrations of quaternary ammonium compounds

Resistance to disinfection agents: Adaptation of P. aeruginosa to sub­ inhibitory concentrations of quaternary ammonium compounds (QACs)

Effects of antibacterial agents and drugs monitored by atomic force microscopy

Adaptation of Pseudomonas aeruginosa to constant sub-inhibitory concentrations of quaternary ammonium compounds

Resistance to disinfection agents: Adaptation of P. aeruginosa to sub­ inhibitory concentrations of quaternary ammonium compounds (QACs)

Resistance to disinfection agents: Adaptation of P. aeruginosa to sub inhibitory concentrations of quaternary ammonium compounds (QACs)

Resistance to disinfection agents: Adaptation of P. aeruginosa to sub inhibitory concentrations of quaternary ammonium compounds (QACs)