Electron microscopy of chloramphenicol-treated Escherichia coli.

Thin sections of Escherichia coli were examined by electron microscopy at sequential intervals after addition and then removal of chloramphenicol. The first changes, occurring at 1 hr after exposure to the drug, were disappearance of the ribosomes and aggregation of the nuclear material toward the center of the bacteria. At 2 hr, aggregates of abnormal cytoplasmic granules first appeared and subsequently increased in size. By 23 hr, amorphous, electron-dense material had accumulated within, and at the periphery of, the nuclear matrix. With the removal of chloramphenicol, the bacteria became normal in appearance, passing through a series of stages that were sequential but not synchronous. At 145 min after removal of chloramphenicol, bacteria were encountered in the process of abnormal division. The influence of deoxyribonucleic acid and ribonucleic acid synthesis, and of energy metabolism, upon the changes seen electron microscopically in chloramphenicol-treated cells, was investigated by selectively inhibiting these functions with hydroxyurea, azauracil, and sodium azide, respectively.