Reversion to Bacillary Form of Proteus mirabilis Spheroplasts Induced by Ampicillin: Scanning Electron Microscopic Study

Bacterial cells of Proteus mirabilis were easily induced to spheroplasts In the liquid medium by the addition of aminobenzylpenlcillin (ampicillin). The spheroplasts were unable to divide, but they were able to reverse to the bacillary forms in the liquid medium that ampicillin was not contained. Four phases of the reversion sequence could be differentiated by scanning electron microscopy. (1) After 1 hr of incubation in ampicillin free medium, some projections arose out of the spheroplasts. The projections grew and elongated. (2) The elongation of them resulted in the morphological changes of spheroplasts, from spherical bodies to long irregular bacillary forms. Some of them elongated straight, and others branched. (3) During further incubation they produced a few constricted parts which seemed to be division sites. (4) The long bacillary form split along the constricted parts, then the parent bacillary forms of Proteus mirabilis were completed.