Rapid detection of antimicrobial activity using flow cytometry

Different antibiotic classes vary considerably in their modes of action and hence in their effects on the bacterial cell. Flow cytometry was used to analyse E. coli cells treated with five antibiotics differing a their modes of action. The ratio of protein content, as measured by fluorescence, to forward light scatter (i.e., FL1:FSC) provided a simple and reliable way of detecting within 2 h of treatment antimicrobial activity at a 0.5 minimum inhibitory concentration. This ability to detect antimicrobial activity rapidly offers considerable advantages in drug research for the rapid detection of novel antimicrobials and may, with further development, find a use in the clinic for rapid susceptibility testing as an aid to the selection of therapy. © 1995 Wiley-Liss, Inc.