Detection by death: A rapid way to detect viable slow-growing microorganisms achieved using microchannel Electrical Impedance Spectroscopy (m-EIS)

Abstract

Based on the insight that only living organisms can be killed (and that killing can proceed much faster than cell-growth), we present an approach for the detection of viable microorganisms that is much faster than currently used culture-based methods. We do so by using microchannel Electrical Impedance Spectroscopy (m-EIS) for real-time detection of cell-death on exposure to a killing-agent. m-EIS relies on the fact that when living-cells with non-zero membrane potentials are exposed to high-frequency AC-field, induced-charges accumulate at the membrane-interface. Cell-death is accompanied by a loss of membrane-potential, and hence charge-storage (capacitance). A proof-of-principle for a clinical-application (detection of living mycobacteria in sputum) is demonstrated. Mycobacterium smegmatis (doubling-time ∼3 hours) and Mycobacterium bovis BCG (doubling-time ∼20 hours) in artificial-sputum are both detected in [Formula: see text]3 hours when exposed to amikacin. Times-to-detection (TTDs) are ∼12 hours and ∼84 hours (3 1/2 days), respectively for culture-based detection using current technologies (BD-MGIT-960[Formula: see text]) for samples containing similar loads of M. smegmatis and M. bovis BCG

Direct-from-sputum rapid phenotypic drug susceptibility test for mycobacteria

“…We have previously demonstrated the use of m-EIS to detect mycobacteria in decontaminated sputum samples: both on the basis of detecting their proliferation (a process taking ~36 hours for M . bovis BCG ) [ 49 ], and a novel “detection by death” approach [ 52 ]. Micro-wells dedicated to implementing these approaches may be incorporated into the same microfluidic cassette to bring together a portable, sensitive, and affordable device to detect M .…”