Nanoscale imaging to quantify electrical property of bacteria

Nanoscale imaging approaches to quantifying the electrical properties of pathogenic bacteria

Ryan Berthelot and Suresh Neethirajan

Biomedical Physics and Engineering Express  (Link

Biofilms are natural, resilient films formed when microorganisms adhere to a surface and form a complex three-dimensional structure that allows them to persist in a wide variety of environments. Readily forming in hospitals and on medical equipment, biofilms are frequent causes of infections and their subsequent complications. Due to the complexity of these structures, systematically studying individual bacterial cells and their interactions with their surrounding environment will provide a deeper understanding of the processes occurring within the biofilm as whole versus bulk population based methods that do not differentiate individual cells or species. Methods based on atomic force microscopy (AFM) are particularly suited to the study of individual cells, but are underutilized for the study of bacterial electrical properties. The ability of electrical currents to impair bacterial attachment is well documented, but to utilize electrical current as an effective antibacterial treatment, it is important to understand the electrical properties of bacteria. Therefore, we used AFM, Kelvin probe force microscopy, and ResiScope (module to perform conductive AFM) to measure the surface potential and conductance of Psuedomonas aeruginosa and methicillin resistance Staphylococcus aureus (MRSA) on gold and stainless steel. This is the first study to directly measure the electrical resistance of single bacterial cells using ResiScope. Our goal was to develop a framework for measuring biological molecules using conductive atomic force microscopy. We found that the average resistance for P. aeruginosa was 135±25 GΩ, while MRSA had an average of 173±16 GΩ. Using KPFM, the surface potential of MRSA shifted from -0.304 V to 0.153 V and from -0.280 V to 0.172 V for P. aeruginosa on gold versus stainless steel substrates, respectively. In an attempt to identify a potential charge carrier, peptidoglycan was also measured with the ResiScope module and shown to have a resistance of 105 GΩ. 

 

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