A fast impedance-based antimicrobial susceptibility test

There is an urgent need to develop simple and fast antimicrobial susceptibility tests (ASTs) that allow informed prescribing of antibiotics. Here, we describe a label-free AST that can deliver results within an hour, using an actively dividing culture as starting material. The bacteria are incubated in the presence of an antibiotic for 30min, and then approximately 10(5) cells are analysed one-by-one with microfluidic impedance cytometry for 2-3min. The measured electrical characteristics reflect the phenotypic response of the bacteria to the mode of action of a particular antibiotic, in a 30-minute incubation window. The results are consistent with those obtained by classical broth microdilution assays for a range of antibiotics and bacterial species. There is an urgent need to develop simple and fast antimicrobial susceptibility tests. Here, Spencer et al. describe a label-free test that can deliver results within an hour, consisting of a 30-min antibiotic treatment followed by single-cell analysis of phenotypic responses with microfluidic impedance cytometry.