In situ potentiometric method to evaluate bacterial outer membrane-permeabilizing ability of drugs: Example using antiprotozoal diamidines

► We introduced a new assay system, combining tyrocidine A and a K+-selective electrode, to evaluate the bacterial outer membrane-permeabilizing ability of drugs. ► The method enabled us to monitor drug action in situ. ► We found that antiprotozoal diamidines, such as diminazene, pentamidine, and 4',6-diamidino-2-phenylindole (DAPI), can increase the permeability of the bacterial outer membrane.