Electrical Broth Micro-Dilution for Rapid Antibiotic Resistance Testing.

Rapid tests to assess the susceptibility of bacteria to antibiotics are required to inform antibiotic stewardship. We have developed a novel test, which measures changes in the impedance of a 100 nanoliter volume of bacterial suspension to determine an "electrical" minimum inhibitory concentration (eMIC). Two representative strains of Klebsiella pneumoniae , Acinetobacter baumannii , Escherichia coli , Pseudomonas aeruginosa, and Staphylococcus aureus were tested against a panel of frontline antibiotics with different modes of action (ciprofloxacin, doxycycline, colistin and imipenem, gentamicin, and ceftazidime). The eMIC measured at 1 h correlated strongly with a standard 24 h microbroth dilution MIC for all combinations of antibiotics and bacteria, allowing strains to be correctly assigned as sensitive or resistant measured in a fraction of the time.