Abstract: We aim at advancing an effective setup for rapid phenotypic Antimicrobial Susceptibility Testing (AST) and discuss the analysis performed at population versus single cell levels. Electrical Impedance Spectroscopy (EIS) is commonly used for functional characterization of living cells. EIS allows direct assessment of membrane integrity and, as such, of the cellular viability status. While entire cellular population can be electrically addressed at once, single-cell EIS analysis is provided either by Impedance Cytometry or by label-free Electrically Modulated Light Microscopy. However, only the latter allows analysis of (single) cell cycle dynamics alterations due to drug exposure. For rapid capturing and concentrating microbial cells from biological samples, we have developed a proprietary immuno-magnetic cell separation assay capable of expediting analyses either merely by EIS, as well as by electrically actuated optical microscopy. Whereas EIS analysis of a cluster (population) of magnetically tagged microorganisms allowed phenotypic AST in just 15 minutes, for thorough assessment of heterogenous microbial cell response to antimicrobials, single-cell assays have to be performed. Adding AC electrical actuation to light microscopy provides label-free, high-resolution images of both optical path and electrical impedance of living cells. These maps relate to the distribution of the refractive index and conductivity, as complementary intrinsic cellular parameters and imaging contrast elements. This multimodal method provides new capabilities for determining both electrical and optical structures of (microbial) cells and their dynamic changes per se, or in response to exposure to antimicrobial drugs. Our presentation will highlight our recent developments in: (1) cell separation, (2) in-situ AST assessment based on EIS fingerprint of magnetically tagged microbial cells as well as (3) of analysis of (single) cell cycle dynamics changes, and related heterogeneities, revealed by Electrically Modulated Light Microscopy. We will emphasize the complementarity between optical (refractive index) and electrical (conductivity) maps/images especially concerning the viability status.
Keywords: EIS, electro-optical microscopy, phenotypic antimicrobial susceptibility testing, electrical and structural fingerprint

Biography: Prof. Eugen Gheorghiu graduated (Bio)Physics at the University of Bucharest, then worked on: (1) developing microscopic models on the dielectric behavior of (non)spheroidal living cells, (2) analyzing cell cycle progression using non-linear modelling, to receive his Ph.D. in theoretical physics with Prof Aureliu Sandulescu in 1994. He then established the biophysics lab within the National Institute of Biotechnology in Bucharest. He was a JSPS fellow at Kyoto University (1996-1997), then established the International Centre of Biodynamics, under UNESCO. During 2003-2009 he coordinated the Master Programme in Biodynamics, within the University of Bucharest, since 2004- he is PhD Advisor, University of Bucharest. His long-standing research interests span developments of electrically modulated optical assays supporting non-invasive analysis of living cell dynamics (per se and exposed to drugs), rapid detection of markers in blood (using portable, multichannel SPR systems), fast point-of-care methods and devices for: (a) sensitive identification & quantitation of microbes, and (b) Phenotypic Antibacterial & Antifungal Susceptibility/Resistance Testing based on immune-magnetic capture, magnetophoresis and electro-optical fingerprinting. He is first author of over 10 international and Romanian patents, and corresponding author of over 50 papers, a recent land-mark relates to high-resolution mapping of the electrical impedance and optical path at nanoscale, based on quantitative phase imaging combined with electrical actuation, reported in Nature-LSA (2021).