The researchers used quantitative electrostatic force microscopy (EFM) in their study, a technique that they recently developed and successfully applied to measure the electrical properties of 3D nano-objects such as nanoparticles and viruses. EFM senses the electrical properties of the whole bacterial cell, including its cytoplasmatic region, and so is able to provide a wealth of information on a bacterium’s electrical response.
In this way, the researchers quantified the electric polarization response of four bacterial types – Lactobacilus sakei, Salmonella Typhimurium, Escherchia coli and Listeria innocua, all of which are of either clinical or industrial relevance – and revealed important differences between Gram-negative and Gram-positive bacteria.
Previous electrical studies – which until now have only been able to be done on bacterial populations involving millions of bacterial cells, and not on single cells – have allowed researchers to detect bacteria in an environment, count and differentiate them, determine their viability, distinguish mutants even among highly similar genotypes, and separate them from other cells. The fact that this new technique allows the measurement of the electrical properties of single cells without the need for separation enables the heterogeneity within a population to be accurately quantified.—
Reference article: Daniel Esteban-Ferrer, Martin A. Edwards, Laura Fumagalli, Antonio Juárez, and Gabriel Gomila (2014). Electric Polarization Properties of Single Bacteria Measured with Electrostatic Force Microscopy. ACS Nano, 8 (10), pp 9843–9849