Flow cytometry of bacteria: cell cycle kinetics and effects of antibiotics.

Flow cytometric determination of the DNA and protein content of E. coli has been carried out by means of a microscope-based flow cytophotometer with a high pressure arc lamp excitation ligh source. Fluorescence (DNA)/light scatter (total cell protein) dual parameter histograms with a resolution cv of 5% were obtained for cells labeled with a combination of mithramycin and ethidium bromide. Histograms of E. coli in rapid and slow exponential growth are presented to exemplify how the cell cycle kinetics of bacteria can be studied in much more detail than has been possible by other methods. Significant effects of chloramphenicol and penicillin on the cell cycle distribution and cell numbers of E. coli cultures were evident after one hour of culture. The data provided information on which parts of the cell cycle and what types of processes were affected by the drug. It appears that flow cytometry may become a valuable tool in studies of the cell cycle of bacteria as well as in clinical drug testing.