RAPID ASSESSMENT OF ANTIBIOTIC EFFECTS ON ESCHERICHIA-COLI BY BIS-(1,3-DIBUTYLBARBITURIC ACID) TRIMETHINE OXONOL AND FLOW-CYTOMETRY

The effects of selected antibiotics on Escherichia coli were studied b y flow cytometry with the fluorescent anionic membrane potential probe bis-(1,3-dibutylbarbituric acid) trimethine oxonol [DiBAC(4)(3)], The actions of azithromycin, cefuroxime, and ciprofloxacin at five times the MIC on E. coli were compared by the traditional CFU assay and flow cytometry, Changes in viable counts of bacteria determined with DiBAC (4)(3) and by flow cytometry following treatment with the antibiotics showed trends similar to those found by the CPU assays. However, viabl e counts determined by flow cytometry following antibiotic treatment w ere 1 to 2 logs higher than those determined by the corresponding CFU assays, All the results obtained by flow cytometry were provided withi n 10 min after sampling, whereas the conventional CPU assay results to ok at least 18 h. The results indicated that flow cytometry is a sensi tive analytical technique that can rapidly monitor the physiological c hanges of individual microorganisms following antibiotic action and ca n provide information on the mode of action of a drug, The membrane po tential probe DiBAC(4)(3) provides a robust flow cytometric indicator for bacterial cell viability.