Yuji KAGEYAMA, Haruna SUEOKA, Akira KIMURA, Masaki SATO, Akira ITO, Tetsuro HORIE, Genki OGATA, Yasuaki EINAGA, Hiroaki SUZUKI, Shingo MURAKAMI
Vol. 13 (2024) p. 90-99

The lipid bilayer membrane of microorganisms exhibits capacitance that can be used to assess the proliferation, reduction, or transformation of these microorganisms by evaluating the permittivity of their lipid bilayer membrane. Traditionally, the effects of pharmacological substances on viruses have been measured indirectly by observing cytopathic effects on cultured cells. Nevertheless, the novel approach that depends on permittivity is anticipated to provide an innovative assay for preliminary screening of potential drugs against microorganisms. In an effort to quantify directly the pharmacological effects of compounds on microorganisms, we devised a method that avoids the indirect pharmacological effects on cultured cells. Instead, this method measures the direct effect by assessing the permittivity induced by the lipid bilayer membrane itself. To validate the effectiveness of our approach, and to demonstrate the feasibility of permittivity measurements in microorganisms, we designed an electrode-replaceable measuring cell using 3D printing technology. Using this measuring cell, we measured permittivity of egg phosphatidylcholine liposomes and yeast cells, both of which exhibit lipid bilayers and are suitable for experimental purposes. We measured the permittivity of a KCl solution, as well as suspension of liposomes or yeast cells in KCl solution. We observed an increase in permittivity within a frequency range of 104-108 Hz, which can be ascribed to the lipid bilayers of the liposomes and yeast cells. Following lysis of liposomes by adding Triton-X 100, we observed a reduction in the enhanced permittivity. Furthermore, when the yeast cell count was reduced by dilution, there was a corresponding decrease in the enhanced permittivity. A decrease in permittivity was also noted in a suspension of yeast cells in KCl solution following heat and enzyme treatments. These results suggest that the permittivity of lipid bilayer membrane can be measured and harnessed to estimate the concentration of microorganisms in a solution. Consequently, we anticipate that this method will be developed as a pioneering assay for early drug screening, given its capacity to evaluate the pharmacological effects of compounds on viruses, without the necessity for cultured cells.